Plio-Pleistocene imprint of natural climate cycles in marine...

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Lebreiro, S. M. 2013. Plio-Pleistocene imprint of natural climate cycles in marine sediments. Boletín Geológico y Minero, 124 (2): 283-305ISSN: 0366-0176

Plio-Pleistocene imprint of natural climate cycles in marine sediments

S. M. Lebreiro

Instituto Geológico y Minero de España, OPI. Dept. de Investigación y Prospectiva Geocientífica. Calle Ríos Rosas, 23, 28003-Madrid, España

[email protected]

AbStRACt

the response of Earth to natural climate cyclicity is written in marine sediments. the Earth is a complex system, as is climate change determined by various modes, frequency of cycles, forcings, boundary conditions, thresholds, and tipping elements. Oceans act as climate change buffers, and marine sediments provide archives of climate conditions in the Earth´s history. to read climate records they must be well-dated, well-calibrated and analysed at high-resolution. Reconstructions of past climates are based on climate variables such as atmospheric composi-tion, temperature, salinity, ocean productivity and wind, the nature and quality which are of the utmost impor-tance. Once the palaeoclimate and palaeoceanographic proxy-variables of past events are well documented, the best results of modelling and validation, and future predictions can be obtained from climate models. Neither the mechanisms for abrupt climate changes at orbital, millennial and multi-decadal time scales nor the origin, rhythms and stability of cyclicity are as yet fully understood. Possible sources of cyclicity are either natural in the form of internal ocean-atmosphere-land interactions or external radioactive forcing such as solar irradiance and volcanic activity, or else anthropogenic. Coupling with stochastic resonance is also very probable.

I provide here, an overview of the cyclicity affecting the Earth on various time scales focussing upon the Plio-Pleistocene and Holocene epochs, together with a compilation of some of the key questions under de-bate, and a number of representative works that illustrate cyclicity in marine sediments.

Key words: cyclicity, millennial-scale, multi-decadal-scale, orbital-scale, Pliocene-Pleistocene

Impronta de la ciclicidad climática natural en sedimentos marinos durante el Plio-Pleistoceno

ResuMen

La respuesta de la Tierra a la ciclicidad natural del clima se encuentra inscrita en los sedimentos marinos. La Tierra es un sistema complejo, en el que el cambio climático viene determinado por varios modos, frecuencia de sus ciclos, causas, condiciones de contorno, puntos irreversibles y elementos de no retorno. Los océanos amortiguan el cambio climático, y preservan en los sedimentos marinos las condiciones climáticas de la historia terrestre. Para su lectura es necesario que los registros estén bien datados, calibrados y analizados a alta resolución. Las reconstrucciones climáticas del pasado se basan en indicadores climáticos, tales como la composición atmosférica, temperatura, salinidad, productividad oceánica y viento, cuya naturaleza y calidad son cruciales. La calidad de los indicadores de paleoclima y paleoceanografía garantiza buenos resultados derivados de la modelización y su validación, y del rigor de las predicciones a partir de los modelos climá-ticos. Los mecanismos que rigen los cambios climáticos a escala orbital, milenaria y multi-decadal no se comprenden en la actualidad en su totalidad, como tampoco se conoce del todo el origen, ritmo y estabilidad de los ciclos. el origen de la ciclicidad climática puede ser natural (interacciones internas entre atmósfera-océano-continente o efecto externo de la radioactividad tal como la irradiancia solar y la actividad volcánica) o antropogénica. Hay que añadir además una alternativa y probable resonancia estocástica.

el presente trabajo aporta una visión de la ciclicidad que afecta a la Tierra, a varias escalas temporales, y contempla las épocas del Plioceno, Pleistoceno y Holoceno. se recopilan algunas de las cuestiones clave que necesitan una mayor perseverancia para su entendimiento y se enumeran trabajos científicos representativos de ciclicidad registrada en el ámbito marino.

Palabras clave: ciclicidad, milenaria, multi-decadal, orbital, Plioceno-Pleistoceno

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Lebreiro, S. M. 2013. Plio-Pleistocene imprint of natural climate cycles in marine sediments. Boletín Geológico y Minero, 124 (2): 283-305

VeRsIOn ABReVIADA en CAsTeLLAnO

Introducción

en la naturaleza abundan los fenómenos que se rigen conforme a patrones repetitivos de cambios climáticos abruptos. entre ellos podrían destacarse: el punto alcanzado por las concentraciones de CO2 en el que la bios-fera y el océano son aún capaces de actuar como sumideros disminuyendo sus niveles en la atmosfera; el crecimiento y colapso alternativo de los glaciares desde el inicio del Pleistoceno (2,6 My) según la insolación en las altas latitudes; el calentamiento rápido del Polo sur cuando del Polo norte súbitamente se desprenden témpanos de hielo y cesa la circulación termohalina (CTH); y la magnitud de eventos extremos de inundacio-nes o sequías acorde con la circulación atmosférica.

Los sedimentos marinos muestran la impronta de la ciclicidad natural orbital (ciclos de 400 000 años (ka), 100 ka, 41 ka y 21 ka) y las respuestas a los cambios climáticos impuestos al sistema Tierra. Aún cuando el origen de estos ciclos no es del todo conocido, han sido considerados orígenes externos y más regulares (cambios de los parámetros orbitales de la Tierra, conocidos como de Milankovitch) e internos y menos regu-lares (dinámica de los glaciares, CTH, ciclo del carbono, etc). La localización de los mecanismos inductores no es exclusiva de la latitud. se ha demostrado que la eccentricidad (400 y 100 ka) rige los períodos glaciales, con procesos focalizados en latitudes altas, aún cuando la oblicuidad (41 ka) es la frecuencia dominante del volumen de hielo en los polos (shackleton, 2000; Paillard y Parrenin, 2004). el CO2 parece jugar un papel importante en esta discrepancia, aunque no resulta fácil cuantificar los limites de sensibilidad del clima y los umbrales de las transiciones de CO2 hacia un calentamiento (Knutti y Hegerl, 2008), dada la incertidumbre en relación al papel de la circulación oceánica en el ciclo del carbono, como afecta el almacenamiento de C a los ciclos, o los niveles de saturación de CO2 que impulsan a un cambio del modo de funcionamiento del sistema. Cuando la insolación disminuye en las latitudes altas (Berger, 1978) (Fig. 1), la precesión (21 ka) refuerza la estacionalidad en las latitudes bajas, supeditando los vientos Alíseos y los Monzones, que a su vez influyen en la circulación oceánica ecuatorial, tropical y de las latitudes subtropicales (deMenocal et al., 1993; Chapman y Maslin, 1999). sin embargo, no es del todo conocido el impacto de los cambios climáticos tropicales en el Atlántico norte (Rosenthal et al., 2003; Oppo et al., 2003).

Las series de paleo-datos integran los mecanismos de inducción y retroalimentación de la ciclicidad cli-mática, y sus procesos, además de revelar el posible impacto antropogénico en la variabilidad climática na-tural (soon y Baliunas, 2003), los cuales parecen estar cambiando los ciclos de larga duración. Los modelos climáticos son frecuentemente usados para simular la complejidad de las respuestas climáticas del sistema (Alverson et al., 2003). el análisis de registros de ciclicidad requiere precaución en relación a su extensión y resolución temporal, sobretodo si abarcan cambios del último siglo y se utilizan para realizar predicciones futuras.

en este artículo se enfocan diferentes ciclicidades y sus orígenes y se enumeran estudios clave y/o representativos en los que claramente se refleja la impronta de la ciclicidad en sedimentos del fondo oceánico.

Variabilidad orbital (105)

Edades glaciales

Los cambios de los parámetros orbitales (Milankovitch) aportan ciclicidades naturales con frecuencias de 400, 100, 41 y 21 ka.

el enfriamiento general del Plioceno desemboca en la Glaciación del Hemisferio norte (GHn) con desarro-llo de glaciares a partir de 2,6 Ma, que marca el inicio del Pleistoceno (Fig. 2). A lo largo de este destacan otras dos transiciones abruptas, acaecidas hace 1,4 Ma y hace 1 Ma, la última de las cuales es denominada Tran-sición del Pleistoceno Medio (TPM) (Lisiecki y Raymo, 2007). este registro Plio-Pleistoceno revela una curva general en forma de sierra con oscilaciones que son de gran amplitud de variaciones de temperatura, de nivel del mar y de concentraciones de CO2 y así como de metano en la atmosfera, correspondientes a los períodos glaciales e interglaciales (GI) del Pleistoceno (Fig. 1). La forma de las oscilaciones es asimétrica, debido a que la construcción de los glaciares tarda 80 ka en producirse y las desglaciaciones son muy rápidas del orden de 10 ka (Lisiecki y Raymo, 2007).

entre las causas de la GHn se encuentran el cambio de la posición de los continentes, el levantamiento tectónico, la creación de suelo oceánico, la circulación oceánica profunda, la reducción de CO2 atmosférico y la insolación. La TPM puede deberse a formación y estabilización de los glaciares, cambios en los márgenes continentales afectados por procesos de (des)glaciación, y/o aumento de los umbrales de insolación.

Las edades de las transiciones son cruciales a la hora de defender ciclicidades y en concreto para el inter-valo Plio-Pleistoceno se han establecido tres cronoestratigrafías: la sPeCMAP de Imbrie et al. (1984) y Raymo (1997); la PIsO-1500RPI de Channel et al. (2008; 2009) y la LR04 de Lisiecki y Raymo (2005).

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Mecanismos y Ciclicidad

elbikki y Rial (2001) exponen en una revisión exhaustiva que la hipótesis de Milankovitch (Hays et al., 1976) mantiene su valor, y que el clima responde de manera linear a las frecuencias de Milankovitch. sin embargo, shackleton (2000) ha demostrado que el ciclo de los 100 ka se encuentra en fase con el C atmosférico, la temperatura del aire en la Antártida y el agua profunda, mientras que el volumen de hielo obedece a una fre-cuencia de 41 ka, desfasada en 6-14 ka de los anteriores. Paillard (2001) también enuncia posibles debilidades de la teoría astronómica clásica, incapaz de explicar cambios climáticos abruptos o la ausencia de cambios orbitales significativos, como la persistencia del ciclo de 100 ka, la transición del ciclo de 41 ka a 100 ka en la TPM, o el estadio isotópico marino (MIs en inglés)-11. A esto, elbikki y Rial (2001) añaden la amplitud de los ciclos GI de 100 ka y la ausencia del ciclo de 400 ka en los últimos 1,2 Ma. Igualmente, se apuntan como nue-vos componentes con potencialidad para influir en los cambios de la ciclicidad las concentraciones de CO2, la productividad oceánica del Polo sur, o la circulación profunda (Paillard, 2001). en la última década, varios estudios han demostrado que los cambios climáticos a escala orbital que afectan al ecuador y a los Trópicos pueden haberse generado en altas latitudes (100 ka y 41 ka) pero también por procesos típicos de bajas latitu-des como los Monzones (ciclo de 21 ka) (deMenocal, 1993; Leuschner y sirocko, 2003; Tjallingil et al., 2008).

son muchos los trabajos que confirman las interacciones entre las ciclicidades orbitales y que están basados en estudios de multi-indicadores (ej. Charles et al., 2010; Martrat et al., 2004; Hernández-Almeida et al., 2012; Tzedakis et al., 2004; deMenocal et al., 1993; Larrasoaña et al., 2003; Abrantes, 2003; Tiedemann y Mix, 2007).

Variabilidad milenaria (103)

Estadios glaciales

Los cambios climáticos abruptos tienen su mejor expresión en los eventos Dansgaard-Oeschger (DO) y Hein-rich (He) (Dansgaard et al., 1993; Johnsen et al., 1992) que irrumpen en el período entre los 110 y 10 ka. se trata de oscilaciones emparejadas que reflejan condiciones extremas de temperatura, con variaciones en el Polo norte de 10ºC/100 años (ePICA project members, 2006; Rousseau et al., 2006). el patrón de ciclicidad identifi-cado inicialmente en el hielo glaciar se repite en los sedimentos del fondo oceánico de todo el Planeta (Bond et al., 1997; revisión por Voelker et al., 2002) (Fig. 3). Y aunque inicialmente se detectaron en el MIs-3, de nivel de mar intermedio (McManus et al., 1999; schulz, 2002; Ganopolsky y Rahmstorf, 2002), se han encontrado también en los estadios estrictamente glaciales como los MIs-6, 8, 10, 12 (ej. McManus et al., 1999; de Abreu et al., 2003; siddall et al., 2007; Margani et al., 2010).


Los DO y He son parte integral del balance térmico bipolar, que produce una respuesta asimétrica entre los dos hemisferios (Broecker, 1994; Blunier et al., 1998; figura 1 de Clark et al., 2007). La mayoría de las modeli-zaciones que soportan esta hipótesis requieren una descarga súbita de agua helada procedente del deshielo de los glaciares del Atlántico norte, que obliga a una reorganización de la circulación oceánica termohalina (AMOC en inglés, Circulación Meridional de Retorno del Atlántico) que oscila entre dos extremos desde el cese completo de su corriente en los He hasta su restablecimiento en los estadios más cálidos (Is, interesta-diales) (sarnthein et al., 1995; stocker y Wright, 1991; Fanning y Weaver, 1997; Manabe y stouffer, 1997; Alley et al., 1999; sakai y Peltier, 1999; Ganopolski y Rahmstorf, 2001). el cese de la formación de agua profunda en el Atlántico norte (en los He), evita que Groenlandia se enfríe en exceso, por lo que la Antártida se calienta y transfiere calor al Polo norte (Clark et al., 2002; Alley et al., 2007; stenni et al., 2010; severinghaus, 2009). entre los posibles mecanismos generadores de los DO y He se cuentan el transporte de calor oceánico a tra-vés del ecuador, la sincronización hielo-océano debido a los cambios del nivel del mar, la inestabilidad de los márgenes continentales que sufrieron procesos de des(glaciación) y el calentamiento subsuperficial (revisión por schmittner et al., 2007). La transmisión de los cambios climáticos que se producen en el Atlántico norte hacia el ecuador es muy rápida, afectando la intensidad de los vientos Alíseos y Monzones, la expansión y migración del cinturón de la Zona de Convergencia Intertropical (ZCIT), y la variación de las temperaturas y oxigenación del océano Pacífico (ej. Timmermann y Goosse, 2004; Zhang y Delworth, 2005).

el ciclo de 1.47 ka (Groots y stuiver, 1997; Bond y Lotti, 1995; Mayewski et al., 1997; Rahmstorf, 2003) es el más publicado para los DO durante el intervalo glacial de 110-10 ka. Los He, que engloban varias parejas de DO, ocurren cada 7 ka (ej. Clark et al., 2007), configurando los ciclos de Bond (Bond et al., 1993) (Fig. 3), que no deben confundirse con las oscilaciones de similar frecuencia pero mucho menor amplitud del Holoceno (Bond et al., 1997). el origen de esta ciclicidad se ha explicado tanto por factores naturales internos (estabilidad de los glacia-res y ciclo hidrológico) como externos (insolación orbital) (Rial y Yang, 2007), además de por la superposición de otros dos períodos de 87 y 210 años en un sistema no-lineal (Braun et al., 2005), o una resonancia estocástica que justifica elementos periódicos de eventos climáticos abruptos cada 1.47 ka (“el reloj” de Rahmstorf, 2003).

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existe una colección enorme de trabajos que manifiesta y valida resultados de modelos climáticos, con registros de diferentes indicadores biogeoquímicos en los sedimentos marinos (ej. Bond et al., 1993; Grousset et al., 1993; Lebreiro et al., 1996; van Kreveld et al., 1996; Little et al., 1997; Vidal et al., 1997; Vidal et al., 1998; Kennett et al., 2000; Cacho et al., 2000; shackleton et al., 2000; Kanfoush et al., 2000; Peterson et al., 2000; Grousset et al., 2001; Pailler y Bard, 2002; elliot et al., 2002; de Abreu et al., 2003; Hendy y Kennett, 2003; Mo-reno et al., 2004; sierro et al., 2005; Voelker et al., 2006; skinner y elderfield, 2007; saikku et al., 2009).

Holoceno

el Holoceno muestra oscilaciones de menor amplitud que los estadios glaciales (revisión por Mayewski, 2004), aunque existe una periodicidad marcadamente similar a los períodos anteriores. su frecuencia apunta también a un valor de 1,470 ka (Bond et al., 1997; 2001), atribuida por la mayoría de los autores a una contri-bución solar y oceánica. Algunos análisis espectrales no convergen sin embargo en un único valor. Debret et al. (2007) separa dos picos de 1 y 2 ka y 1,5 ka, asignados independientemente a un origen solar y/o oceánico, respectivamente. Otros autores encuentran recurrencias en torno a 900 años (schulz y Paul, 2000) o múltiples frecuencias de diferente significación estadística (sarnthein et al., 2003).

Variabilidad multi-decadal (101-102)

Las oscilaciones climáticas de período corto controlan, por ejemplo, precipitaciones, inundaciones, sequías, huracanes, o la productividad pesquera costera y oceánica, con un impacto importante en la sociedad y en la economía.

existen varios modos de variabilidad multi-decadal bien identificados en el sistema climático actual, unos de ámbito global como la de el niño-Oscilación del sur (ensO en sus siglas en inglés; Gershunov y Barnett, 1998; enfield et al., 2001), la Oscilación del Atlántico norte (nAO; Hurrell, 1995), y la Oscilación Multi-decadal Atlántica (AMO; Kerr, 2000; enfield et al., 2001), y otros más regionales como la Oscilación Decadal del Pací-fico (PDO; Mantua et al., 1997; nPO; Gershunov y Barnett, 1998), la Oscilación del Ártico (AO; Ambaun et al., 2001; Marshall et al., 2001), o el Modo Anular del sur (sAM; Kidson, 1988; Arblaster y Meehl, 2006). estos son índices que representan la variación de fenómenos atmosféricos de temperatura y presión, dependientes de datos instrumentales, y por tanto con una extensión temporal limitada a los últimos 150 años. Afortunada-mente esta variabilidad de alta frecuencia queda registrada, entre otros archivos, en los sedimentos marinos (Fig. 4), alargando su escala temporal hacia el pasado, lo que permite la validación y calibración de los datos y afianza la robustez de las series climáticas.


La ensO (cálida) condiciona el clima del Pacífico norte y del Atlántico norte, siendo inversamente relacionada con los Monzones de la India (débil) (Kumar et al., 1999). Además presenta una ciclicidad de 3-7 años (Dong y sutton, 2002) e intervalos especialmente intensos como los de 1982–83 y 1997–98 (Wolter y Timlin, 1998). La nAO muestra una amplitud máxima de presión sobre Islandia y las Azores, y repercute en los Vientos del Oeste a través del Atlántico norte hacia europa (Hurrell, 1995; 2001; 2003; Rodwell et al., 1999). Posee una pe-riodicidad de 2-4 (u 8) años (Cook et al., 2002). La AMO crea anomalías de temperatura en el Atlántico norte, de modo que valores positivos se correlacionan con temperaturas más altas, menos precipitaciones y en con-secuencia períodos de sequía (Kerr, 2000; Feng et al., 2009). La AMO muestra un patrón más homogéneo que la nAO. el análisis espectral apunta a frecuencias de 11 años (Lohmann et al., 2004), 70 años (schlesinger y Ramankutty, 1994; Delworth y Mann, 2000; Andronova y schlesinger, 2000), o el ciclo Gleissberg de irradiancia solar de 90 y 210 años (Ogurtsov et al., 2002; Dergachev, 2004).

se ha recurrido a varios mecanismos para explicar las altas frecuencias de los ciclos de variabilidad multi-decadal, tanto de origen interno (CTH, acumulación de hielo-deshielo, vientos, migración latitudinal de la ZCIT, convección de aire tropical) (Delworth et al., 1993; 1997; Timmermann et al., 1998; Delworth y Mann, 2000; Marshall et al., 2001; Yu et al., 2002; Latif et al., 2004; Cheng et al., 2004; Vellinga y Wu, 2004; Zhang y Delworth, 2005; Dai et al., 2005; Knight et al., 2005; Dima y Lohmann, 2007; Biastoch et al., 2008), como de origen externo (irradiancia solar y erupciones volcánicas) (Ottera et al., 2010), e incluso resonancia estocástica (Delworth y Greatbatch, 2000; Dima y Lohmann, 2007).

La variabilidad climática multi-decadal (Fig. 3) queda plasmada en un número notable de publicaciones tanto como respuesta a cambios climáticos en el ámbito marino (ej. sicre et al., 2008; Boessenkool et al., 2007) como en el continental (ej. Bartels-Jonsdottir et al., 2006; Lebreiro et al., 2006; Alt-epping et al., 2009). el registro de cambios climáticos continentales en medio marino no es exclusivo de la escala multi-decadal, sino también de la milenaria (ej. sánchez Goñi et al., 2002; Jullien et al., 2007; Lebreiro et al., 2009; Romero et al., 2011) y de la orbital (ej. Harris y Mix, 1999).

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Introduction

the discovery of abrupt climate changes occurring in accordance with different time scales and the need to explain them have introduced the concepts of exceeded critical thresholds, tipping points and hysteresis in relation to the recovery, stability, and continuity of climatic patterns of variability (bradley et al., 2003; Lenton et al., 2008). Many phenomena contribute to repeatitious patterns of abrupt climate change in nature: CO2 concentrations have reached points at which biosphere and ocean have still been

able to sequester and lower atmospheric levels once more; ice-sheets have grown and declined since the onset of the Pleistocene (2.6 Myr) following high-lat-itude insolation changes; the south pole has warmed quickly while the north pole ice-sheets were disman-tled into armadas of icebergs and the tHC (thermo-haline circulation) ceased; and the magnitude of river floods and droughts have reflected persistent atmospheric patterns. Marine sediments show the imprint of orbital (400-kyr-thousand of years, 100-kyr, 41-kyr, 21-kyr), millennial (1.5-kyr), multi-decadal (80-yr-years, 3-7 yr) cycles, and the palaeoclimate

Interacción entre diversos modos de variabilidad multi-decadal

Hay una interacción global entre los diversos modos de variabilidad multi-decadal puestos en evidencia, por ejemplo, en los siguientes trabajos: la AMO determina la variabilidad en el Pacífico norte a través de los tró-picos por medio de la ZCIT (Dong y sutton, 2002; Zhang y Delworth, 2007; Dima y Lohmann, 2007); la ensO impone sequía en el Pacífico Oeste, calor en el norte de los estados unidos de América y humedad en el sur, impidiendo el desarrollo de huracanes en el Atlántico. La ensO intensa (el niño) es consistente con una nPO positiva, asociada con una anomalía fría en el Pacífico noroeste, y al revés para La niña (fase contraria a el niño) (Gershunov y Barnett, 1998).

Superposición de las diferentes escalas de variabilidad

La ciclos orbitales, milenarios y multi-decadales interaccionan, probablemente, porque el origen y mecanis-mos que producen sus ciclos son parcialmente comunes; por ejemplo, la CTH funciona y sufre cambios a escala orbital, milenaria y multi-decadal. el ciclo de 21 ka atraviesa los 2,6 Ma, del Plioceno al Pleistoceno, aún cuando se produce una transición del dominio del ciclo de 41 ka al de 100 ka (Becker et al., 2006). Los ciclos sub-orbitales y milenarios prevalecen no solo a lo largo de los períodos glaciales (McManus et al., 1999; de Abreu et al., 2003; Becker et al., 2006; Margani et al., 2010), sino también como sub-estadiales en los períodos interglaciales (McManus et al., 1994; McManus et al., 1999; Chapman et al., 1999; Oppo et al., 2001; Tzedakis et al., 2004; schaefer et al., 2005; Desprat et al., 2007; 2008). Además Tzedakis et al. (2004) sugieren que la du-ración de los Interglaciales pueda obedecer a la variabilidad milenaria, y Pena et al. (2008) a la multi-decadal de la ensO. La migración del cinturón de la ZCIT opera de igual modo en la ensO que en los He (Leduc et al., 2009). Las condiciones actuales de la ensO se correlacionan también con las de los estadiales fríos de los DO en las latitudes altas, mientras La-niña lo hacen con los interestadiales (stott et al., 2002), el Período Cálido Medieval (PCM) (Khider et al., 2011) y el eIM5e (Pelejero et al., 2003). La fase positiva de la nAO predomina a lo largo del PCM, mientras la fase negativa lo hace durante la Pequeña edad del Hielo (Abrantes et al., 2005; Trouet et al., 2009).

Inducción antropogénica en el cambio climático

no es de esperar que los modos de la variabilidad climática analizada permanezcan constantes en amplitud y frecuencia en el futuro (Alverson et al., 2003; Lorenz et al., 2006; Koutavas et al., 2006; Clement, 2000; Goosse et al., 2006). entre otras evidencias, podría apuntarse la contaminación atmosférica que altera el equilibrio de la irradiancia del Planeta (ej. Rayner et al., 2003; Delworth et al., 2007; Latif et al., 2007), la probabilidad del cese de la CTH (Wood et al., 2003), la expansión de la ZCIT (Koutavas et al., 2006), o el aumento de la concentración de CO2 que puede intensificar o debilitar los ciclos GI (Goodwin et al., 2009; Lenton et al., 2008).

Conclusiones

Los sedimentos marinos aportan información sobre la ciclicidad climática natural impuesta al Planeta. Las series climáticas vienen revelando en sus análisis espectrales la alta probabilidad de que los diversos modos de variabilidad obedezcan a una combinación de mecanismos, que funcionan de modo similar y actúan a di-ferentes escalas. Conocer el porqué de los cambios de ciclicidad es crítico para su aplicación en predicciones climáticas futuras, así como para discernir el posible impacto antropogénico en la variabilidad.

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forcing responses. Although the origin of this cyclici-ty remains uncertain, many external forcings such as secular changes in the Earth orbital – Milankovitch´ parameters, where oscillatory modes are more regu-lar, and internal forcings such as ice-sheet dynam-ics, tHC circulation, and the carbon cycle, which are more irregular, have been proposed.

It is generally accepted that the eccentricity caus-ing a 100-kyr cycle, drives the northern hemisphere ice ages and build-up of ice-sheets, but that the 41-kyr obliquity cycle is the dominant frequency in ice volume (Shackleton, 2000); CO2 arose as the promoter of the 100-kyr signal (Shackleton, 2000; Paillard and Parrenin, 2004). Quantifying the limits of climate sensitivity and rates of CO2 transients to warming is not easy howev-er (Knutti and Hegerl, 2008), because of uncertainties about the role of ocean circulation in the carbon cycle, how carbon storage affects cycles, or the existence of a threshold level of CO2 that switches to a different mode. When insolation decreases at high-latitudes (berger, 1978), precession, a 21-kyr cycle strengthens seasonality at lower latitudes, driving trade winds and monsoons, which in turn influence equatorial, subtropical and mid-latitudinal oceanic processes (deMenocal et al., 1993; Chapman and Maslin, 1999). Moisture and heat transferred polewards across the equator preconditions northern-hemisphere ice-sheet growth and water temperature changes (Ruddiman and McIntyre, 1981; Dahl et al., 2005). Nevertheless, the impact of changes in the North Atlantic upon the climate in the tropics and vice-versa is not really un-derstood (Rosenthal et al., 2003; Oppo et al., 2003).

Palaeo-data series integrate forcings and feedbacks and the processes operating on them. Palaeo-re-cords also show natural forcing mechanisms prior to the anthropogenic forcing, allowing us to distin-guish and calibrate the superimposition of human intervention in the variability (Soon and baliunas, 2003). Models are useful tools, but have limited ca-pability to represent accurately the true variability of complex climate-system responses (Alverson et al., 2003). Analysing cyclicity requires prudence with re-gard to the length of records and time scales, par-ticularly during the last century, where records aim for future predictions. It seems certain though that natural climate forcing is sensitive and vulnerable to anthropogenic activity in terms of future changes to long-lasting past cycles.

In this paper I offer an approach to different cy-clicities and their origins, together with references to representative studies into marine sediments and their relationship with responses to climate systems.

Orbital variability (105)

Ice ages

Milankovitch cycles (Milankovitch, 1941) depend upon natural orbital oscillations of the Earth and the amount of insolation (incoming solar radiation it receives). Milankovitch cycles have three quasi-periodicities (EtP parameters) of about 100, 41 and 21 kyr; eccentricity (the Earth´s orbit around the Sun), obliquity or tilt (axial tilt of the Earth in relation to the plane of the ecliptic), and precession of the equinoxes (the rotation of the Earth´s axis, which impinges upon the seasons) (Fig. 1). Eccen-tricity may also be reflected in a long period of 400 kyr.

General cooling in the Pliocene (Zachos et al., 2001) resulted in the onset of the northern-hemisphere glaci-ation (NHG) with a growth of the ice-sheets beginning some 2.6 Myr ago (Pleistocene) (Fig. 2). During the Pleistocene two abrupt climate transitions took place, one at 1.4 Ma-million years and another around 1 Ma bP; this latter is called the mid-Pleistocene transition (MPt) (Lisiecki and Raymo, 2007). the Plio-Pleistocene reveals a saw-tooth curve, with changing variability (cf. Figure 4 in Lisiecki and Raymo, 2005; stacked ben-thic d18O record) into the Pleistocene Glacial-Intergla-cial (GI) oscillations, which record the highest ampli-tude in terms of global temperatures, sea-level, and greenhouse-gas parameters. their shapes are highly asymmetric because the building-up of ice-sheets (glaciation) takes a very long time (~80 kyr) whilst deglaciation, on the other hand, is comparatively fast (~10 kyr) (Lisiecki and Raymo, 2007). the speed of de-glaciation coincides with the rapid release of CO2 into the atmosphere (Ruddiman and Raymo, 2003; De Sae-deleer et al., 2012).

Amid the causes triggering this major climate NHG change are variable continental positions, tectonic uplift, decreased rates of sea-floor spreading, deep ocean circulation, reduction in atmospheric CO2 lev-els and insolation. Causes for the MPt are outlined in Lisiecki and Raymo (2007) and include ice-sheets for-mation and stabilization, changes in ice margins and an increase in insolation thresholds.

the timing of the major climate terminations is es-sential and three timescales are often used, all based upon the d18O of benthic foraminifera and tuned to an astronomical curve, where terminations are tight-ly linked to increases in summer 65ºN radiation, ie. deglaciations or warming at high northern latitudes: SPECMAP (Imbrie et al., 1984; Raymo, 1997), covering 800 kyr; PISO-1500 RPI, based on the geomagnetic pa-laeo-intensity (Channel et al., 2008; 2009) for the last 1.5 Myr; and LR04 (Lisiecki and Raymo, 2005) for the Pliocene-Pleistocene (5.3 Myr).

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Figure 1. Natural orbital oscillations of the Earth (Milanko-vitch cycles) recorded in marine sediments. Periodicities are marked by the EtP parameters: (A) eccentricity (the Earth´s orbit around the Sun), (b) obliquity or tilt (the axial tilt of the Earth in relation to the plane of the ecliptic), and (C) preces-sion (rotation of the Earth´s axis). (D) is solar forcing at 65ºN latitude, and (E) glacial-interglacial d18O stack in benthic fora-minifera of the North Atlantic (Lisiecki and Raymo, 2005). build with data available from NOAA/NGDC Paleoclimatol-ogy Program, boulder CO, USA (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/), and IGbP PAGES/World Data Center for Paleocli-matology. Original references: berger and Loutre (1991), and Lisiecki and Raymo (2005).Figura 1. Variabilidad orbital natural de la Tierra (ciclos de Mi-lankovitch) registrados en los sedimentos marinos. Las perio-dicidades se identifican como eTP: (A) eccentricidad (órbita de la Tierra alrededor del sol), (B) Oblicuidad (inclinación del plano axial de la Tierra en relación con la eclíptica del sol), y (C) Precesión (rotación del eje de la Tierra). (D) es la Irradian-cia solar y (e) Registro Glacial-Interglacial medio de d18O de foraminíferos bentónicos del Atlántico norte (Lisiecki y Ray-mo, 2005). Datos disponibles en nOAA/nGDC Paleoclimato-logy Program, Boulder CO, usA (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/), o IGBP PAGes/World Data Center for Paleocli-matology, Referencias bibliográficas originales: Berger y Lo-utre (1991) y Lisiecki y Raymo (2005).

Figure 2. Past 5.5 Myr record of d18O in benthic foraminifera with obvious changes in cyclicity at the onset of the northern hemisphere glaciation (2.6 Ma) and the mid-Pleistocene transition (~1 Ma) towards the glacial/interglacial modes. Data available from NOAA/NGDC Paleoclimatology Program, boulder CO, USA, or IGbP PAGES/World Data Center for Paleoclimatology. Original data from Lisiecki and Raymo (2005). Figura 2. Cambios de la ciclicidad para el intervalo del Plio-Pleistoceno (últimos 5,5 Ma) en los isótopos (d18O) de foraminíferos bentónicos. el inicio de la Glaciación del Hemisferio norte se produce hace 2,6 Ma. La Transición del Pleistoceno Medio ocurre hace ~1 Ma y da lugar al paso de una frecuencia dominante de 41 ka a otra de 100 ka, con las oscilaciones correspondientes a las Glaciaciones-Desglaciaciones bien marcadas. Datos disponibles en nOAA/nGDC Palaeoclimatology Program, Boulder CO, usA. Referencia bibliográfica original: Lisiecki y Raymo (2005).

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Mechanisms and cyclicity

It was always thought that the 100-kyr cycle repre-sented the major component of northern-hemisphere ice volume changes. Since the mid 90´s, however, many authors have questioned this. In an exhaustive revision, Elbikki and Rial (2001) concluded that the Milankovitch hypothesis arisen by Hays et al. (1976) still holds good, the climate system responding non-linearly to all Milankovitch frequencies and the ec-centricity signal bring deeply imbedded in the marine time-series data.

Shackleton (2000) emphasised the difficulty in-volved in explaining the predominant cycle in terms of orbital eccentricity (both small in amplitude and late in phase), and the non-linearity of the response of the ice-sheets to the 100-kyr period of orbital eccen-tricity when the precession dominated 65ºN summer insolation record is used as a forcing (model of Imbrie and Imbrie, 1980). He demonstrated that atmospheric carbon, air temperature (Vostok, Antarctica) and deep-water are in phase with orbital eccentricity (dominant 100-kyr period), while ice volume shows a dominant obliquity peak and lags the three previous variables by 5 to 14 kyr (cf. Figure 5 in Shackleton, 2000). More-over, Shackleton infers that the influence of CO2 con-centration in the atmosphere generates the effect of orbital eccentricity. Elbikki and Rial (2001) reacted to the implied linearity of the system response to pre-cession and obliquity, by claiming that Rial and Ana-clerio (2000) had found obliquity to be non-linear. the problem of linearity versus non-linearity is still a moot point (cf. review by Elbikki and Rial, 2001). An addi-tional issue, discussed by the same authors, is wheth-er insolation is driven or considered independently in the models. In general, the models range from those that assume self-sustaining internal oscillations with no relation to insolation to those insolation-driven producing oscillations by non-linear coupling of high-er frequency, or non-linear resonance.

Paillard (2001) challenged the classical astronomical theory and suggested a new paradigma. He contested the sufficiency of linear and weakly linear systems to fully explain the dynamics of the 100-kyr cycles, intro-ducing the concept of climate thresholds, encouraged by the increasing number of observations in the long term marine and ice records becoming available, such as the glacial 110-10-kyr abrupt switches, the chang-ing patterns of long series of GI terminations and the atmospheric concentrations of carbon dioxide and methane. Paillard examined several pitfalls in the clas-sical astronomical theory of palaeoclimate, which he identified as the “100-kyr problem” (although the main cyclicity in the palaeoclimatic record is close to 100-

kyr, there are no significant orbitally induced changes in the radioactive forcing of the Earth within this fre-quency range), the “mid-Pleistocene transition prob-lem” (i.e. the change from a 41-kyr to a 100-kyr domi-nant periodicity at about 1 Ma occurred without major changes in orbital forcing or in the Earth’s configura-tion), and the “stage 11 problem” (the most prominent GI transition occured at a time of minimal orbital varia-tions). Elbikki and Rial (2001) identified additional awk-ward issues: the wide amplitude of the 100-kyr ice age cycles; the variation in glacial cycle duration over the past 800 kyr; the absence of significant spectral pow-er in the 400-kyr cycle over the past 1.2 Ma; and the presence of non-orbital spectral peaks in the climate record. Paillard (2001) outlines potential components of the climate system, such as atmospheric CO2 con-centration, Southern Ocean productivity, and global deep-water circulation that may play an important role in the climate cycles, apart from ice-sheets.

Many authors have tried to resolve these draw-backs, particularly during the last decade (cf. benzi et al., 1982; Muller and MacDonald, 1997; Ridgwell et al., 1999; tziperman and Gildor, 2003; Loutre and berger, 2003; Paillard and Parrenin; 2004; EPICA community members, 2004; berger et al., 2005; Huybers, 2007; Luthi et al., 2008; Loulergue et al., 2008; bintanja and van de Wal, 2008; De Saedeleer et al., 2012). Lisiecki and Raymo (2005, 2007) examined the response to changes in d18O in benthic foraminifera in 57 marine records and found powerful obliquity (41-kyr) and pre-cession (21-kyr) throughout the whole 5.3 Ma, but with increasing sensitivity to obliquity before 1.4 Ma, and precession after 2.6 Ma. Although 100-kyr cycles have been dominant for the last 0.8 Myr no abrupt climate transition was encountered in the obliquity and pre-cession responses; new findings and differences that need further explanation. these authors state that GI cycles are orbitally forced and paced rather than self-sustained, as supported by Huybers (2007, 2009), which has served to arouse new controversy.

GI equatorial climate is controlled by both high- latitude forcing processes (dominant 100 and 41-kyr cycles), mainly during glacials, when North Atlantic SSts are cold and enhance dust transport and arid conditions, but also by low-latitude precessional mon-soon forcing (dominant 21-kyr cycles) during intergla-cials, particularly before 2.5 Myr bP (deMenocal, 1993; Leuschner and Sirocko, 2003; tjallingil et al., 2008).

Marine palaeo-climate data series

Apart from the key papers referred to above, other authors confirm the interaction of orbital cycles in multi-proxy series such as C and O gradients (Charles

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et al., 2010); biomarkers (Martrat et al., 2004); plank-tonic foraminifera (Hernández-Almeida et al., 2012); and pollen (tzedakis et al., 2004). Precessional low-latitude orbital forcing at Atlantic, Mediterranean and Pacific Equatorial sites have been identified by their eolian and biogenic components (deMenocal et al., 1993); terrigenous and magnetic sediment properties (Larrasoaña et al., 2003); and diatoms and phytoliths (Abrantes, 2003; tiedemann and Mix, 2007).

Millennial scale variability (103)

Glacial stages

Abrupt climate change finds its best defence in the so-called Dansgaard-Oeschger (DO) and Heinrich (HE) events in palaeoclimate records. DO events were first detected in Greenland ice-cores (Dansgaard et al., 1993; Johnsen et al., 1992) during the last glacial 110 – 10 kyr in a number of 25 paired oscillations known as

Greenland stadials (GS) and interstadials (GIS) (EPICA project members, 2006; Rousseau et al., 2006). Hei-nrich events (Heinrich, 1988) numbered H0 (Younger Dryas) to H6, from the most recent to the oldest (bond et al., 1997), bear witness to extremely cold conditions and occur between every packet of three DO events. DOs reflect a characteristic pattern of abrupt warming of approximately 10ºC (Greenland) into a interstadial (in decades) and more gradual cooling (in centuries) into severe stadials, though every event lasted for ap-proximately 1 to 3 thousand years. Even though ice-core records were initially established as references, DO and HE events have been widely reported all over the North Atlantic in marine-sediment cores (eg. Fig. 3) with sufficient sedimentation rate and sample reso-lution (many compiled in Voelker et al., 2002). these millennial-scale saw-tooth pulses seem to have oc-curred preferably during a period of intermediate global ice volume [marine isotope stage, (MIS)-3], between extremely cold glacial and warm interglacial modes (MIS 2-4) (McManus et al., 1999; Schulz, 2002; Ganopolsky and Rahmstorf, 2002), and to some ex-

Figure 3. Millennial-scale abrupt climate variability (11-80 ka) of core site MD95-2042 (Shackleton et al., 2000) on the North Atlantic, Portu-guese Margin, rescaled to SFCP (Shackleton et al., 2004), showing (b) planktonic and (C) benthic d18O isotopes. Correlation between marine sediments and ice-cores: (A) Greenland´ GRIP d18O (SMOW) isotopes (Johnsen et al., 1992) and (D) Antarctica Vostok d18O (SMOW) isotopes (Jouzel et al., 1999). Numbers 1-20 are Dansgaard-Oeschger climate oscillations, HE stands for Heinrich events, bA for bolling-Allerod, YD for Younger Dryas, and A for Antarctica warm events (blunier and brook, 2001). bond cycles shown by curved lines in Greenland´s profile (bond et al., 1993). Data available from www.esc.cam.ac.uk/pop/popdata/.Figura 3. Variabilidad climática milenaria de isótopos de O de foraminíferos planctónicos (B) y bentónicos (C), entre los 11 y 80 ka en el Atlántico norte, en el testigo MD95-2042 del margen de Portugal (shackleton et al., 2000), corregido para la escala temporal sFCP por shackleton et al. (2004). Correlación de registros de sedimentos marinos con hielo polar: d18O (sMOW) de la perforación GRIP de Groenlan-dia (Johnsen et al., 1992) (A) y d18O (sMOW) de la Vostok de la Antártida (Jouzel et al., 1999) (D). Los números de 1-20 indican oscilaciones climáticas Dansgaard-Oeschger, He los eventos Heinrich, BA indica Bolling-Allerod, YD es el Younger Dryas, y A los episodios cálidos de la Antártida (Blunier y Brook, 2001), desfasados con los Is cálidos de Groenlandia. Los ciclos de Bond se encuentran representados en el registro (A) (Bond et al., 1993). Todos los datos se encuentran disponibles en www.esc.cam.ac.uk/pop/popdata/.

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tent in other glacials such as MIS-6, 8, 10 and 12 (cf. McManus et al., 1999; de Abreu et al., 2003; Siddall et al., 2007; Margani et al., 2010).

In the Antarctic ice-cores for the same time period of MIS 4-2 oscillations depict less abrupt changes and more squarer shapes (cf. Figure 4 in Shackleton et al., 2000). Inter-pole comparison of the Greenland DO-HE sequence pattern with the Antarctica counter-parts (EPICA, 2006) (Fig. 3), reveals three important features: 1) rapid cooling and warming in Greenland; 2) the absence of rapid warmings in the Antarctic; and 3) the north and south poles out-of-phase, linked with the meridional overturning circulation (MOC) and at-mospheric circulation.

Mechanisms

the ocean MOC, termed earlier tHC or “the great conveyor belt” (broecker, 1991; reviews in Alley, 2007 and Lozier, 2010), is an important component of the Earth´s climatic system. the MOC can be defined as a “system of surface and deep currents encompassing all ocean basins. It transports large amounts of wa-ter, heat, salt, carbon, nutrients and other substances around the globe, and connects the surface ocean and atmosphere with the huge reservoir of the deep sea” (Schmittner et al., 2007).

the idea that fresh water discharged into the North Atlantic leads to the reorganization of oceanic circu-lation and heat transport coupled with atmospheric changes was championed by broecker (1994; Alley, 2007, and references herein), and has been greatly expanded upon since then. theoretical models have shown that only a small perturbation (weak fresh-water forcing) is required to trigger abrupt changes in the MOC (Stocker and Wright, 1991; Fanning and Weaver, 1997; Manabe and Stouffer, 1997; Sakai and Peltier, 1999; Ganopolski and Rahmstorf, 2001), and so the key issue revolves around finding the mecha-nisms that influence the NA freshwater budget. Atmo-spheric response to North Atlantic oceanic change is very rapid, affecting the strength of the trade winds and upwelling, the migration of intertropical conver-gence zone (ItCZ), the intensity of the Asian monsoon and temperatures and ventilation in the North Pacific (cf. timmermann and Goosse, 2004; Zhang and Del-worth, 2005).

Hundreds of coupled ocean-atmospheric models of different complexity give the response of ocean cir-culation to freshwater and temperature forcing and generally imply the existence of thresholds and hys-teresis in the strength of the MOC (cf. review in Rahm-storf et al., 2005). the climate system exhibits mul-

tiple modes of operation between the two extremes of MOC-on and MOC-off. the mode switches vary de-pending upon the place and strength of sinking cold, and dense water: 1) in the modern ocean (Holocene-style interglacial) the NADW at high-latitudes sinks to great depths with intense overturning, 2) in the glacial ocean, reduced sinking to intermediate depths occurs at lower latitudes; and 3) at HE, there is no sinking wa-ter and overturning collapses (Sarnthein et al., 1995; Alley et al., 1999; Rahmstorf, 2002; Stocker, 2002). For a large freshwater input, involving a substantial re-lease of icebergs such as that observed in the North Atlantic during HE, deep-water formation is temporar-ily switched off, causing no great cooling in Green-land, but warming in Antarctica, with heat transmitted to the northern hemisphere.

Inter-hemispheric synchronization of ice records between Greenland and Antarctica, which is decisive to an understanding of the role of global ocean cir-culation, has been reliably achieved on the basis of based on atmospheric gas concentrations (bender et al., 1994; blunier and brook, 2001; blunier et al., 2007). the resulting picture synchronises maximum HE cooling in Greenland with maximum warming in Antarctica. Furthermore, during the last deglaciation, the northern Oldest Dryas – bolling/Allerod – Younger Dryas sequence matches up with warming Antarctic Cold Reversal – warming in the southern hemisphere (blunnier et al., 1997; Stenni et al., 2001; Clark el al., 2002), which is clearly out-of-phase. there is also a one-to-one coupling of inter-hemispheric climate events with changes in the overturning of strength and heat transport (Skinner et al., 2007). these obser-vations support the bipolar see-saw climatic model, which is fairly well established nowadays (cf. Clark et al., 2002; Alley et al., 2007; Severinghaus, 2009; Stenni et al., 2010) based on the tHC and the conveyor belt paradigma (broecker, 1998; Stocker, 1998; Alley et al., 1999). the basic mechanism assumes that the shutting-off of tHC triggers rapid cooling in the north and warming in the south, because heat is no longer transported northward. the rate of deep-water forma-tion and perturbation of the tHC is responsible for mil-lennial scale events. DO and HE events are, therefore, an integral part of the thermal bipolar seesaw balance that produces the asymmetric response between the hemispheres (blunier et al., 1998; figure 1 of Clark et al., 2007). Among the possible mechanisms that may trigger DO-HE events are cross-equatorial ocean heat transport, coupled ice-ocean due to sealevel changes, and ice-shelf instability and subsurface warming (cf. review by Schmittner et al., 2007).

Given chronostratigraphic uncertainties, signs of phasing beyond synchrony are even more complex to

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resolve. It is important though to decipher which pole leads rapid climate change. Steig and Alley (2002) claim that only 50% of the Greenland-Antarctica behaviour is in antiphase, and is particularly in phase during cool-ing. Although most authors validate the see-saw model in their works, it is not yet clear whether the North dials the South (cf. Hinnov et al., 2002; Stocker, 2000; Ganop-olski and Rahmstorf, 2001; Stocker and Johnsen, 2003; Schmittner et al., 2003; Knutti et al., 2004), or viceversa (cf. bender et al., 1994; Charles et al., 1996; blunier et al., 1997; Knorr and Lohmann, 2003; Huybers, 2004). Or perhaps it remains an ambiguous, unsolved question (Skinner et al., 2007).

Cyclicity

the cycle of 1 470-kyr deduced from the ice-cores by Groots and Stuiver (1997) seems to be regular and reliable for DO events during the 110-10-kyr glacial period (bond and Lotti, 1995; Mayewski et al., 1997; Rahmstorf, 2003), and is strongly imprinted in marine cores.

A long-term cooling trend that envelopes around three DO oscillations and concludes in an extreme stadial, an HE event, is named a bond cycle (bond et al., 1993); the following cycle begins abruptly with an outstandingly warm interglacial (Fig. 3). HEs occur ap-proximately every 7 kyr (cf. Clark et al., 2007). but still spectral analysis often fails to notice any clear peri-odicity, possibly due to imprecise time scales (Alley, 2007).

Internal forcing of the periodicity of abrupt climate events such as DOs and HEs remains uncertain, main-ly because of the complex interaction between the stability of ice-sheets and the hydrological cycle (pre-cipitation, run-off, iceberg discharge). Some authors have suggested that external forcing such as orbital insolation might influence the timing of abrupt DO cli-mate changes through frequency (or phase) modula-tion (Rial and Yang, 2007). braun et al. (2005) go even further and claim the reproduction of DO events in ab-sence of the 1.5-kyr cycle in the forcing and spectrum because this number represents the superimposition of two freshwater cycles with shorter periods of 87 and 210 yrs in a non-linear system.

Some models, on the other hand, assumed a sto-chastic resonance mechanism to explain periodic el-ements of abrupt climatic events. Rahmstorf (2003) claims that DOs are discrete events paced by a regu-lar 1 470-kyr cycle (the clock) rather than being cycles themselves. Using a simple event-detection algo-rithm, this period falls into the 95% confidence inter-val. the presence of other secondary maxima at 3 and 4.5-kyr in noise amplitude in the Greenland ice-core

data suggests that the stochastic resonance variabil-ity in the glacial climate is suboptimal for triggering events of time evolution, amplitude, special pattern and interspike intervals such as DO events (Ganopol-ski and Rahmstorf, 2002). the authors outline, how-ever, that stochastic resonance would be limited to switches between deep-water production sites rather than thermo-haline on-off regimes. If a stochastic sys-tem does exist, given its regularity its origin must be outside the Earth´s system because oscillatory modes within the Earth are more irregular.

the cause of periodic oscillation remains uncertain, but weak internal signals of noise and periodic forc-ing possibly combine to cause transitions when the phase of the periodic forcing is favourable (Alley et al., 2001). Rial and Yang (2007) add that in nature, DOs could result from a combination of convection, turbu-lence and stochastic resonance.


the connection between ice and the ocean surface was made in the North Atlantic by bond et al. (1993), later recognised together in the surface- and deep-ocean at one site in the Iberian margin by Shackleton et al. (2000), and further verified by Saikku et al. (2009) in the Pacific.

A huge number of studies have resorted to different proxy-variables and generated a collection of marine data-sets in which the Earth´s system clearly responds to millennial cyclicity. Many authors have validated ocean-atmospheric models and integrated real ob-servations and simulations in an attempt to improve future predictions regarding climate change, among whom are: Grousset et al., 1993; Lebreiro et al., 1996; van Kreveld et al., 1996; Little et al., 1997; Vidal et al., 1997; Vidal et al., 1998; Kennett et al., 2000; Cacho et al., 2000; Shackleton et al., 2000; Kanfoush et al., 2000; Peterson et al., 2000; Grousset et al., 2001; Pailler and bard, 2002; Elliot et al., 2002; de Abreu et al., 2003; Hendy and Kennett, 2003; Moreno et al., 2004; Sierro et al., 2005; Voelker et al., 2006; Skinner and Elderfield, 2007; or Saikku et al., 2009.

Climate biogeochemical proxies operate in the same way for long-lived GIs than short-lived inter/stadials cli-mate changes because ocean-circulation patterns are common irrespective of time scales. the tHC is behind the orbital and millennial scales. becker et al. (2006) maintain that the 21-kyr and millennial cycles prevailed around 2.5 Ma bP despite the transition from the 41-kyr-dominated glacial cycles of the late Pliocene to the 100-kyr cycles of the late Pleistocene. Suborbital and mil-lennial scale cycles are pervasive not only throughout

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glacials (McManus et al., 1999; de Abreu et al., 2003; becker et al., 2006; Margani et al., 2010), but also during substadials of interglacial stages (McManus et al., 1994; McManus et al., 1999; Chapman et al., 1999; Oppo et al., 2001; tzedakis et al., 2004; Schaefer et al., 2005; Desprat et al., 2007; 2008). Persistent 1-3-kyr cycles throughout MIS 5-7-9-11-13 support the development of this type of cyclicity in the absence of large ice-sheets, emphasiz-ing that other factors apart from ice volume, such as ocean-ice interactions and mid- and deep-water play an important role in amplifying the suborbital signal in any ocean (Oppo et al., 2001). What also emerges is that although the broad timing of interglacials is consistent with orbital theory their specific duration may be dic-tated by millennial variability (tzedakis et al., 2004).

Holocene stage

Relatively less abrupt climatic events than that of last glacial period also happened worldwide dur-ing the Holocene (last 11.5 cal kyr bP) (cf. review by Mayewski, 2004); the common 1 470-kyr cycle emerg-es throughout its marine palaeoclimate records (bond et al., 1997). In the Holocene, the term bond cycle is often used for the periodicity of ~1.5 kyr after bond et al. (1997) in which ice-rafted quartz and red-stained grains appear in marine sediments, creating confu-sion with the last glacial terminology of the 7-kyr-bond cycle (referred to above).

the origin of the ~1.5-kyr pacing in the Holocene is far from consensual, although a large number of authors cite solar effects and the MOC as being the most probable origins of this variability (cf. review by Mayewski, 2004). Debret et al. (2007), applying wavelet analysis (WA), which is appropriate for non-stationary variability, demonstrated that during the Holocene combined forcing mechanisms with vari-able contribution over time would account for the observed oscillations. Solar forcing would explain the 1-kyr and 2-kyr cycles and oceanic forcing the 1.5-kyr cycle, arguing against bond and co-authors´s interpretation of solar output governing the quasi-periodic 1.5-kyr cycle (2001), because this signal can be split into the 1-kyr and 2.5-kyr cycles by Fourier transform blackmann-tuckey and WA. Palaeoclimate proxies studied in marine sediments suggest a sig-nal close to the 1.5-kyr (bianchi and McCave, 1999; Chapman and Shackleton, 2000; Giraudeau et al., 2000), which probably contains a relative combina-tion of both of the previous forcing mechanisms, or others (atmospheric NAO, Giraudeau et al. 2000; current intensity, bianchi and McCave, 1999; geo-magnetic field, St-Onge et al., 2003). WA also shows

that the 2.5-kyr cycle is continuous throughout the Holocene whilst ~1.5-kyr cycle dominates the record before it.

Ganopolski and Rahmstorf (2001) followed the pres-ence of the ~1.5-kyr period throughout the Holocene but its signature is very weak because it is not ampli-fied by the ocean circulation instability typical of gla-cial times. Schulz and Paul (2002) report a significant, recurrent 900-yr harmonic signal component in the Holocene variability; they suggest that climate cycles can be described as damped oscillations, triggered by cooling events at 8.3 ka and 4.7 ka, with an underlying mechanism behind that might transit from the glacial to the Holocene. Many other authors (cf. Sarnthein et al., 2003) have put forward multiple periodicities of variable significance.

Centennial and multi-decadal scale variability (101-102)

Short-term oscillations of multi-decadal (30-80 yr), decadal (8-12-yr), and interannual (<8-yr) variabil-ity have been forcing responses in rainfall, river floods, droughts, hurricanes, coastal upwelling and ocean productivity, and sea level, among oth-ers, and have therefore had a great ecological and socioeconomic impact on climate changes at the human scale.

Several modes of variability have been established for the modern climate system, such as those of glob-al impact like El Niño-southern oscillation (ENSO) (Gershunov and barnett, 1998; Enfield et al., 2001), the North Atlantic oscillation (NAO) (Hurrell, 1995), the Atlantic multi-decadal oscillation (AMO) (Kerr, 2000; Enfield et al., 2001), and other more regional ones, such as the Pacific Decadal oscillation (PDO) (Mantua et al., 1997) also known as the North Pacific oscilla-tion (NPO) (Gershunov and barnett, 1998), the Arctic oscillation (AO) (Ambaun et al., 2001; Marshall et al., 2001), and the southern annular mode (SAM) (Kidson, 1988; Arblaster and Meehl, 2006). these indices are atmospheric temperature and pressure phenomena defined in instrumental climate and weather data, and therefore their records are limited to instrumental coverage over about the last 150 years. Fortunately these high-frequency modes are also archived in lon-ger-term multi-decadal to centennial scale data series such as historical documents, tree rings, shell rings, ice-cores and corals, as well as varved sediments in lakes and sediments in marine environments (Fig. 4), thus extending the records back in time, and allowing the assessment, calibration, and robustness of multi-decadal variability.

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Mechanisms and cyclicity

ENSO interdecadal variability has a strong impact on the climates of North Pacific and North Atlantic. typical El Niño-events show low pressure over the northeast Pacific, dry northwest and wet southwest. the (warm) ENSO is inversely related to the (weak) Indian summer monsoon (Kumar et al., 1999). Lags in ENSO and the monsoons have also been investi-gated (Webster and Yang, 1992). the basic physics of the ENSO cycle is reasonably well known (tudhope and Collins, 2003), although some aspects remain poorly understood. the ENSO varies considerably in strength and frequency, it was particularly strong, for example, in 1982–83 and again in 1997–98 (Wolter and timlin, 1998). Its cyclicity tends to be one of 3 to 7 years (Dong and Sutton, 2002).

NAO is associated with changes in the surface westerlies across the North Atlantic towards Europe. the NAO index is determined from the difference in sea-level pressure between winters with larger values than 1 and -1 (Hurrell, 1995; 2001; Rodwell et al., 1999). A positive phase is associated with strong westerly winds over the subpolar gyre, leading to enhanced ocean-to-atmosphere heat fluxes. the wider ampli-

tudes of NAO occur at the subpolar (Iceland) and trop-ical (Azores) North Atlantic. An up-to-date compilation can be found in Hurrell et al. (2003). the NAO has a periodicity of 2 to 4 (or 8) years (Cook et al., 2002).

the AMO is marked by a persistent, long-term pat-tern of alternations of warm and cold sea surface tem-perature (SSt) anomalies in the North Atlantic basin and is more properly defined as the first rotated em-pirical orthogonal function (EOF) of the non-ENSO global SSt field (Mestas-Nuñez and Enfield, 2001). Although this mode shows maximum amplitudes in the Atlantic basin, it also includes a positively cor-related multi-decadal oscillation in the North Pacific (Minobe, 1997). During warm (cold) phases, the en-tire North Atlantic ocean shows positive (negative) SSt anomalies, meaning less precipitation and con-sequent droughts (Kerr, 2000; Feng et al., 2009). the AMO has been reconstructed for the last few centu-ries (Gray et al., 2004; Mann and Park, 1995) as well as being identified in several proxy records (Shabalova and Weber, 1999; Stocker and Mysak, 1992; Mann et al., 1995; Delworth and Mann, 2000; Lohmann et al., 2004). It shows a more homogeneous pattern than the NAO, with positive or negative anomalies spanning the whole North Atlantic. Spectral analyses of climat-

Figure 4. Multi-decadal scale climate variability. (A) North Atlantic oscillation Index-winter (Hurrell, 2003), and (b) deep-ocean flow speed (sortable-silt proxy used for changes in Iceland-Scotland overflow water, ISOW) on the eastern flank of the Reykjanes Ridge (core RAPID-21-12b) for the last 230 years. NAO Index Data provided by the Climate Analysis Section, NCAR, boulder, USA, Hurrell (2003), and Sortable Silt from NOAA/NGDC Palaeoclimatology Program, boulder CO, USA. Original reference: boessenkool et al. (2007). Figura 4. Variabilidad climática multi-decadal. (A) Índice de la Oscilación del Atlántico norte para los meses de invierno (Hurrell, 2003), y (B) velocidad de la corriente Iceland-scotland Overflow Water (IsOW), obtenida por medio del Sortable Silt, en el testigo RAPID-21-12B, situado en el flanco este de la Cordillera de Reykjanes, durante los últimos 230 años. Las curvas muestran una notable correlación entre la fase negativa de la nAO y una mayor velocidad del flujo de la IsOW. Datos del Index de la nAO tomados de la Climate Analysis section, nCAR, Boulder, usA, Hurrell (2003), y Sortable Silt de la nOAA/nGDC Palaeoclimatology Program, Boulder CO, usA. Referencia bibliográ-fica original: Boessenkool et al. (2007).

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ic time-series show a significant peak at around 70-yr (Schlesinger and Ramankutty, 1994; Delworth and Mann, 2000), as well as around the 90-yr and 210-yr bands of the Gleissberg solar irradiance cycle (Ogurt-sov et al., 2002; Dergachev, 2004) and the 11-yr cycle (Lohmann et al., 2004).

Several mechanisms both internal and external have been identified to explain these high-frequency cycles such as the tHC, sea ice switches, melting ice, wind, latitudinal shifts in the ItCZ and tropical air con-vection, or solar irradiance and volcanic eruptions, apart from stochastic drivers.

Most coupled atmosphere-ocean models involve tHC fluctuations as the internal driver of multi-dec-adal variability in the Atlantic ocean (Delworth et al., 1993; 1997; timmermann et al., 1998; Delworth and Mann, 2000; Marshall et al., 2001; Latif et al., 2004; Cheng et al., 2004; Dai et al., 2005; Knight et al., 2005). A strong (weak) Atlantic MOC leads to a warm (cold) AMO phase. In a simulation by timmermann et al. (2005) the tHC shutdown in the North Atlantic accom-panied a reduction in variability in the ENSO because of a deepening of the mean zonal tropical Pacific ther-mocline. biastoch et al. (2008) have suggested that the dynamics of the Agulhas leakage at the southern tip of Africa contributes to the MOC signal in the sub- and tropical Atlantic at a similar magnitude to that of the northern source in their influence on multi-decadal variability.

In their model to reproduce MOC multi-decadal variability Vellinga and Wu (2004) lay emphasis upon air-sea coupling, where a stronger MOC during a warmer phase in the Atlantic provoked a northerly shift in the ItCZ and fresher water input to the tropi-cal North Atlantic. Yu et al. (2002) and others focussed on the impact of surface heat flux and wind stress in the Indian Ocean on the ENSO cycle over the Indo-Pacific Ocean region. Dima and Lohmann (2007) in-troduced the sea-ice response to wind forcing, with a thermo-haline circulation adjustment to freshwater forcing, the SSt response to it, oceanic adjustment in the North Pacific and the time scale of the associated multi-decadal cycle. both these latter authors and Del-worth and Greatbatch (2000) state however that given the decadal-scale memory of a two-component atmo-sphere–ocean system, a stochastic forcing applied to the tHC would also suffice to yield multi-decadal peri-odic climatic evolution, regardeless of sea-ice dynam-ics.

Meanwhile, Schlesinger and Ramankutty (1994) proposed that the AMO is probably internally driven by deterministic processes, an idea supported by the numerical experiments of Andronova and Schlesinger (2000), who produced 70-yr cycles not generated by

external forcing. Ottera et al. (2010), however, evoked other externally imposed mechanisms such as natu-ral climate changes in solar irradiance and volcanic eruptions, which affect the amount of radiation trans-mitted, reflected and absorbed by the atmosphere, as forcings to drive phasing of northern hemisphere at-mospheric circulation and multi-decadal variability in the tHC. Solar modulation has also been proposed by Ogi et al. (2003), Ogurtsov et al. (2002), or Lohmann et al. (2004) among others.

Overall, mechanisms proposed among others by Delworth et al. (1993, 1997, 2006), timmermann et al. (1998), timmermann and Goosse (2004), Vellinga and Wu (2004), Zhang and Delworth (2005), Jungclaus et al. (2005), Zhang and Vallis (2006) and Dima and Lo-hmann (2007), share common features including tHC variations, ocean–atmosphere interactions, North Pa-cific manifestations, and hemispheric atmospheric variations.


Some additional cases, not already mentioned, where marine series record multi-decadal variability, are clearly those to the north of Iceland, where SSt con-curs with bottom currents in the North Atlantic and titanium series in the Cariaco basin, which are in turn connected with low-latitude ItCZ changes over the last 4.5 kyr (Sicre et al., 2008); or the correlation shown by boessenkool et al. (2007) between more vigorous Iceland-Scotland overflow water (ISOW) and a nega-tive NAO index for the last 230 years (Fig. 3), with its implications for the Atlantic MOC (AMOC).

Furthermore, continental climate is also reflected in marine- sediment cyclicity according to their pollen, coastal diatoms, biomarkers, eolian and riverine com-ponents, on a centennial scale (cf. bartels-Jonsdottir et al., 2006; Lebreiro et al., 2006; Alt-Epping et al., 2009). but marine sites recording land-sea link vari-ability are also common on millennial (cf. Sánchez Goñi et al., 2002; Jullien et al., 2007; Lebreiro et al., 2009; Romero et al., 2011), and orbital (cf. Harris and Mix, 1999) scales.

Connection between all modes of multi- and decadal variability

Are therefore all decadal variability modes connect-ed? What is the role of the MOC in connecting modes of decadal timescales? Is sea ice in the North Atlantic linked with the ItCZ?

Attempts to answer questions about interaction between the various modes of short-term variability

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are contained in many works. Zhang and Delworth (2007) questioned the influence of the AMO upon North Pacific variability modes such as the PDO, and used a climate model to simulate an ensemble-mean that suppresses North Pacific variability and internal-ly generated ENSO teleconnections, but did show the AMO forcing North Pacific multi-decadal variability. ENSO events, on the contrary, impose dry conditions in the western Pacific, warmer than average condi-tions in the northern United States and wetter than average conditions to the south, suppressing hurri-cane development in the Atlantic. Climatic anoma-lies tend to be weak and spatially incoherent dur-ing low North Pacific oscillation (NPO)–El Niño and high NPO–La Niña winters; typical El Niño patterns are strong and consistent during the high phase of the NPO, associated with an anomalous cold north-western Pacific, and vice-versa during La Niña (Gers-hunov and barnett, 1998).

Dima and Lohmann (2007) and Dong and Sutton (2002) summarize how the multi-decadal signal is transferred from the Atlantic to the Pacific through the tropics (Dima and Lohmann, 2004) via the ItCZ. Fur-thermore, by means of atmospheric teleconnections it is transmitted from the tropics to the North Pacific (Seager et al., 2001). Here it is amplified by a local positive feedback resulting from ocean–atmosphere interactions, with a delay of several years (Peng and Robinson, 2001; Wu et al., 2003). Nevertheless, the mid/high-latitude atmosphere in the northern hemi-sphere can also be involved in transferring the multi-decadal signal from the Atlantic to the Pacific basin.

Overlap with other time-scales

As seen above, orbital and millennial cyclicities often interact. the same is true for the millennial and multi-decadal cycles according to many types of overlap-ping mode, some of which are mentioned here.

Analogous to DO cycles, modern ENSO conditions correlate with millennial-scale stadials at high-lati-tudes, whereas La Niña conditions correlate with in-terstadials (Stott et al., 2002). Similarly, more frequent long-term extreme NAO positive (negative) phases have been found to have influenced the mediaeval warm period (MWP) and little ice age (LIA) periods (cf. Abrantes et al., 2005; trouet et al., 2009), and La Niña-events were more frequent during the MWP (Khider et al., 2011) and MIS5e (Pelejero et al., 2003).

Positive and negative NAOs are dominant in two different phases within HEs in the mid-latitude Atlan-tic (Naughton et al., 2009). In the tropical latitudes, on the other hand, ItCZ southern shifts coherent with

rainfall changes on a millennial HE scale challenge analogous present-day ENSO variability (Leduc et al., 2009). In the same vein as these latter authors, Visser et al. (2003) also stress the importance of the tropical Pacific region in driving orbital rather than millennial GI cycles, although in a way similar to that in which the ENSO regulates poleward heat and water vapour fluxes. Pena et al. (2008) emphasise the relevance of ENSO-like dynamics on the causes of glacial termina-tions.

Climate change and anthropogenic forcing – changes in cyclicity?

there is no reason to expect that the modes of climate variability will remain constant in frequency and am-plitude in the future (cf. Alverson et al., 2003; Lorenz et al., 2006; Koutavas et al., 2006; Clement, 2000; Goosse et al., 2006). We still know little about their centres of action or impact and about how these modes may have developed in the past under different boundary conditions. Atmospheric pollution has altered the ra-dioactive balance of the Earth, making the MOC and anthropogenic forcings to the SSt in the Atlantic dur-ing the 20th century, for example, difficult to discern (cf. Rayner et al., 2003; Delworth et al., 2007; Latif et al., 2007).

Wood et al. (2003) comment about the evolution of the AMOC, writing, “Rapid or irreversible tHC shut-down is considered a low-probability (but high-im-pact) outcome; some climate models of intermediate complexity do show the possibility of such events. the question of the future of the tHC is beset with con-ceptual, modelling and observational uncertainties”. Koutavas et al. (2006) demonstrated the importance of the position of the ItCZ in modulating the ENSO to influence its future evolution conditioned by changes in atmospheric patterns.

As far as the relationship between CO2, carbon ocean storage and its chemical partitioning in the sea water are concerned, Goodwin et al. (2009) find that radioactive forcing of the climate is more sensitive to carbon perturbations now than at any time dur-ing the last 400 kyr. therefore, detecting the proxim-ity of some tipping points implies an early warning of system changes (Lenton et al., 2008) and determines alterations in the strengthening or weakening of cy-cles.

Mitchell et al. (2006) went further in pointing out the occurrence of extreme events in the future due to hu-man-induced climate change, resulting in a non-linear evolution of the MOC, ice sheets and methane release at high latitudes.

298


Conclusions

Marine records of palaeo-events provide insights into the Earth’s past climate variability. the results of spectral analyses reveal a probable combination of multiple modes driven by more than one mechanism. Similar mechanisms seem to function and integrate in a complex system, yielding periodical responses and cyclic patterns regardless of their time-scale. As the past is relevant to future predictions, understanding the modes of cyclic changes is critical, as is discern-ing the real capacity of anthropogenic activities to in-terfere in these modes. If GI climate cycles are very large, DO abrupt climate events are faster, and multi-decadal climate cycles concern human standards of life, in an equally global way.

Acknowledgements

I acknowledge the expert advice of two anonymous referees, who gave their time to detect caveats and flows in the original manuscript.

References

Abrantes, F. 2003. A 340,000 year continental climate record from tropical Africa news from opal phytoliths from the equatorial Atlantic. earth and Planetary science Letters, 209,165-179.

Abrantes, F., Lebreiro, S., Rodrigues, t., Gil, I., bartels-Jóns-dóttir, H., Oliveira, P., Kissel, C., and Grimalt, J.O. 2005. Shallow-marine sediment cores record climate variabil-ity and earthquake activity off Lisbon (Portugal) for the last 2000 years. Quaternary science Reviews, 24 (23–24), 2477–2494.

Alley, R.b., Clark, P.U., Keigwin, L.D., and Webb, R.S. 1999. Making sense of millennial scale climate change. In: Mechanisms of Global Climate Change at Millennial Time scales, Clark, P.U., Webb, R.S., and Keigwin, L.D. (eds.), Washington, DC, American Geophysical Union, 385–394.

Alley, R.b., Anandakrishnan, S., and Jung, P. 2001. Stochas-tic Resonance in the North Atlantic. Paleoceanography, 16 (2), 190-198.

Alley, R.b. 2007. Wally was right: predictive ability of the North Atlantic “Conveyor belt” hypothesis for abrupt cli-mate change. Annual Review of earth and Planetary sci-ences, 35, 241-172.

Alverson, K.D., bradley, R.S., and Pedersen, t.F. 2003. Paleo-climate, Global Change, and the Future. IGbP-PAGES, Springer-Verlag, 229 pp.

Alt-Epping, U., Stuut, J.-b.W., Hebbeln, D., Schneider, R. 2009. Variations in sediment provenance during the past 3000 years off the tagus River, Portugal. Marine Geology, 261, 82–91.

Ambaum, M.H.P., Hoskins, b.J., and Stephenson, D.b. 2001. Arctic Oscillation or North Atlantic Oscillation?. Journal of Climate, 14, 3495–3507.

Andronova, N.G., and Schlesinger, M.E. 2000. Causes of global temperature changes during the 19th and 20th centuries. Geophysical Research Letters, 27 (14), 2137.

Arblaster, J.M., and Meehl, G.A. 2006. Contributions of Ex-ternal Forcings to Southern Annular Mode trends. Jour-nal of Climate, 19, 2896-2905.

bartels-Jónsdóttir, H.b., Knudsen, K.L., Abrantes, F., Lebrei-ro, S., and Eiríksson, J. 2006. Climate variability during the last 2000 years in the tagus Prodelta, western Iberian Margin: benthic foraminifera and stable isotopes, Marine Micropaleontology, 59, 83–103.

becker J., Lourens, L.J., and Raymo, M.E. 2006. High-frequency climate linkages between the North Atlantic and the Mediterranean during marine oxygen isoto-pe stage 100 (MIS100). Paleoceanography, 21, PA3002, doi:10.1029/2005PA001168.

bender, M., Sowers, t., Dickson, M.-L., Orchardo, J., Grootes, P., Mayewski, P.A., and Meese, D.A.1994. Climate correla-tions between Greenland and Antarctica during the past 100,000 years. nature, 372, 663– 666.

benzi, R., Parisi, G., Sutera, A., and Vulpiani, A. 1982. Stochas-tic resonance in climatic change. Tellus, 34 (1), 10–16.

berger, A.L. 1978. Long term variations of caloric solar radia-tion resulting from the Earth’s orbital elements. Quater-nary Research, 9, 139–167.

berger, A., and Loutre, M.F. 1991. Insolation values for the climate of the last 10 million years. Quaternary science Reviews, 10 (4), 297-317.

berger, A., Mélice, J.L., and Loutre, M.F. 2005. On the origin of the 100-kyr cycles in the astronomical forcing. Pale-oceanography, 20, 4019-36.doi:10.1029/2005PA001173.

bianchi, G., and McCave, N.I. 1999. Holocene periodicity in North Atlantic climate and deep-ocean flow south of Ice-land. nature, 397, 515-517.

biastoch, A., böning, C.W., and Lutjeharms, J.R.E. 2008. Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation. nature, 456, 489-92.

bintanja, R., and van de Wal, R.S.W. 2008. North American ice-sheet dynamics and the onset of 100,000-year glacial cycles. nature, 454, 869-872.

blunier, t., Schwander, J., Stauffer, b., Stocker, t., Dallebach, A., Indermuhle, A., and tschumi, J. 1997. timing of the Antarctic Cold Reversal and the atmospheric CO2 increase with respect to the Younger Dryas event. Geophysical Re-search Letters, 24 (21), 2683- 2686.

blunier, t., Chappellaz, J., Schwander, J., Dallenbach, A., Stauffer, b., Stocker, t.F., Raynaud, D., Jouzel, J., Clausen, H.b., Hammer, C.U., and Johnsen, S.J. 1998. Assynchrony of Antarctic and Greenland climate change during the last glacial period. nature, 394, 739-43.

blunier, t., and brook, E.J. 2001. timing of millennial-scale climate change in Antarctica and Greenland during the last glacial period. science, 291 (5501), 109–112.

blunier, t., Spahni, R., barnola, J.M., Chappellaz, J., Louler-gue, L., and Schwander, J. 2007. Synchronization of ice core records via atmospheric gases. Climate of the Past Discussions, 3 (1), 365-381.

299


boessenkool, K.P., Hall, I.R., Elderfield, H., and Yashayaev, I. 2007. North Atlantic climate and deep-ocean flow speed changes during the last 230 years. Geophysical Research Letters, 34, L13614, doi:10.1029/2007GL030285.

bond, G., broecker, W., Johnsen, S., and McManus, J. 1993. Correlations between climate records from North Atlantic sediments and Greenland ice. nature, 365, 143-147.

bond, G.C., and Lotti, R. 1995. Iceberg discharges into the North Atlantic on millennial time scales during the last glaciation. science, 267, 1005-1010.

bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., de-Menocal, P., Priore, P., Cullen, H., Hajdas, I., and bonani, G. 1997. A pervasive millennial-scale cycle in North Atlan-tic Holocene and glacial climates. science, 278 ( 5341), 1257–1266.

bond, G., Kromer, b., beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-bond, R., Hajdas, I., and bonani, G. 2001. Persistent solar influence on North At-lantic climate during the Holocene. science, 294, 2130-2136.

bradley, R.S., Alverson, K., and Pedersen, t.F. 2003. Challen-ges of a changing Earth: past perspectives, future con-cerns. In: Alverson, K., bradley, R.S., and Pedersen, t.F. (eds.), Paleoclimate, global change and the future. Sprin-ger Verlag, berlin, 163–167.

broecker, W.S. 1991. the great ocean conveyor. Oceanogra-phy, 4 (2), 79-89.

broecker, 1994. Massive iceberg discharge as triggers for global climate-change. nature, 372, 421-424.

broecker, W.S. 1998. Paleocean circulation during the last deglaciation: A bipolar seesaw?. Paleoceanography, 13, 119–121.

Cacho, I., Grimalt, J.O., Sierro, F.J., Shackleton, N., and Ca-nals, M. 2000. Evidence for enhanced Mediterranean thermohaline circulation during rapid climatic coolings. earth and Planetary science Letters, 183, 417-429.

Channell, J.E.t., Hodell, D.A., Xuan, C., Mazaud, A., and Stoner, J.S. 2008. Age calibrated relative paleointensity for the last 1.5 Myr at IODP Site U1308 (North Atlantic). earth and Planetary science Letters, 274, 59–71.

Channell, J.E.t., Xuan, C., Hodell, D.A. 2009. Stacking pa-leointensity and oxygen isotope data for the last 1.5 Myr (PISO-1500). earth and Planetary science Letters, 283, 14–23.

Chapman, M.R., and Maslin, M.A. 1999. Low latitude forc-ing of meridional temperature and salinity gradients in the subpolar North Atlantic and the growth of glacial ice sheets. Geology, 27, 875-878.

Chapman, M.R., and Shackleton, N.J. 1999. Global ice-vol-ume fluctuations, North Atlantic ice-rafting events, and deep-ocean circulation changes between 130 and 70 ka. Geology, 27, 795-798.

Chapman, M.R., Shackleton, N.J., and Duplessy, J.-C. 2000. Sea surface temperature variability during the last gla-cial–interglacial cycle: assessing the magnitude and pat-tern of climate change in the North Atlantic. Palaeogeog-raphy, Palaeoclimatology, Palaeoecology, 157, 1–25.

Charles, C.D., Lynch-Stieglitz, J.L., Ninnemann, U.S., and Fairbanks, R.G. 1996. Climate connections between the hemisphere revealed by deep sea sediment core-ice core

correlations. earth and Planetary science Letters, 142, 19–27.

Charles, C.D., Pahnke, K., Zahn, R., Mortyn, P.G., Ninnemann, U., and Hodell, D.A. 2010. Millennial scale evolution of the Southern Ocean chemical divide. Quaternary science Re-views, 29, 399–409.

Cheng, W., bleck, R., and Rooth, C. 2004. Multi-decadal ther-mohaline variability in an ocean–atmosphere general cir-culation model. Climate Dynamics, 22 (6-7), 573-590.

Clark, P.U., Pisias, N.G., Stocker, t.F., and Weaver, A.J. 2002. the role of the thermohaline circulation in abrupt climate change. nature, 415, 863–69.

Clark, P.U., Hostetler, S.W., Pisias, N.G., Schmittner, A., and Meissner, K.J. 2007. Mechanisms for an 7-kyr climate and sea-level oscillation during marine isotope stage 3. In: Schmittner, A., Chiang, J.C.H., Hemming, S.R. (eds.), Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Overturning, AGU Mono-graph, Vol. 173, American Geophysical Union, Washing-ton DC, 392.

Cook, E.R., D’Arrigo, R.D., and Mann, M.E. 2002. A well-ve-rified, multiproxy reconstruction of the winter North At-lantic Oscillation Index since ad 1400. Journal of Climate, 15, 1754-64.

Dahl, A. broccoli, A.J., and Stouffer, R.J. 2005. Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: A tropical Atlantic perspective. Climate Dynamics, 24, 325-346.

Dai, A., Hu, A., Meehl, G.A., and Washington, W.M. 2005. At-lantic thermohaline circulation in a coupled general circu-lation model: unforced variations versus forced changes. Journal of Climate, 18, 3270-3293.

Dansgaard, W. 1993. Evidence for general instability of past climate from a 250 kyr ice-core records. nature, 364, 218–220.

de Abreu L., Shackleton, N.J., Schönfeld, J., Hall, M., and Chapman, M. 2003. Millennial-scale oceanic climate vari-ability off the Western Iberian margin during the last two glacial periods. Marine Geology, 196, 1-20.

Debret, M., bout-Roumazeilles, V., Grousset, F., Desmet, M., McManus, J.F., Massei, N., Sebag, D., Petit, J.-R., Copard, Y., and trentesaux, A. 2007. the origin of the 1500-year cli-mate cycles in Holocene North-Atlantic records. Climate of the Past Discussions, 3, 569–575.

Delworth, t.L., and Greatbatch, R.J. 2000. Multidecadal ther-mohaline circulation variability driven by atmospheric surface flux forcing. Journal of Climate, 13 (9), 1481-95.

Delworth, t.L., and Mann, M.E. 2000. Observed and simulat-ed multidecadal variability in the Northern Hemisphere. Climate Dynamics, 16, 661–676.

Delworth, t.L., Manabe, S., and Stouffer, R.J. 1993. Inter-decadal variability of the thermohaline circulation in a coupled ocean–atmosphere model. Journal of Climate, 6, 1993–2011.

De-Menocal, P.b., Ruddiman, W.F., and Pokras, E.M. 1993. In-fluences of high- and low-latitude processes on African terrestrial climate: Pleistocene eolian records from Equa-torial Atlantic Ocean Drilling Program Site 663. Paleocea-nography, 8 (2), 209-242.

300


Delworth, t.L., Manabe, S., and Stouffer, R.J. 1997. Multi-decadal climate variability in the Greenland Sea and surrounding regions: a coupled model simulation. Geo-physical Research Letters, 24 (3), 257-260.

Delworth, t.L., broccoli, A.J., Rosati, A., Stouffer, R.J., balaji, V., beesley, J.A., Cooke, W.F., Dixon, K.W., Dunne, J., Dunne, K.A., Durachta, J.W., Findell, K.L., Ginoux, P., Gnanadesikan, A., Gordon, C.t., Griffies, S.M., Gudgel, R., Harrison, M.J., Held, I.M., Hemler, R.S., Horowitz, L.W., Klein, S.A., Knut-son, t.R., Kushner, P.J., Langenhorst, A.R., Lee, H.-C., Lin, S.-J., Lu, J., Malyshev, S.L., Milly, P.C.D., Ramaswamy, V., Russell, J., Schwarzkopf, M.D., Shevliakova, E., Sirutis, J.J., Spelman, M.J., Stern, W.F., Winton, M., Wittenberg, A.t., Wyman, b., Zeng, F., and Zhang, R. 2006. GFDL’s CM2 Glob-al Coupled Climate Models. Part I: Formulation and Simula-tion Characteristics. Journal of Climate, 19, 643–674.

Delworth, t.L., Zhang, R., and Mann, M. 2007. Decadal to cen-tennial variability of the Atlantic from observations and models. In: Schmittner, A., Chiang, J.C.H., Hemming, S.R. (eds.), Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Overturning, AGU Monograph, Vol. 173, American Geophysical Union, Washington DC, 131-148.

Dergachev, V.A. 2004. Manifestation of the long-term so-lar cyclicity in climate archives over 10 millennia. In: Stepanov, A.V., benevolenskaya, E.E. and Kosovichev, A.G. (eds.), Multi-Wavelength Investigations of solar Ac-tivity, IAU Symposium, Vol. 223, Cambridge University Press, Cambridge, UK, 699-704.

De Saedeleer b., Crucifix, M., and Wieczorek, S. 2012. Is the astronomical forcing a reliable and unique pacemaker for climate? A conceptual model study. Climate Dynamics, DOI: 10.1007/s00382-012-1316-1.

Desprat, S., Sánchez Goñi, M.F., Naughton, F., turon, J.-L., Duprat, J., Malaizé, b., Cortijo, E., and Peypouquet, J.-P. 2007. Climate variability of the last five isotopic intergla-cials: direct land-sea-ice correlation from the multiproxy analysis of North-Western Iberian margin deep-sea cores. In: Sirocko, F., Claussen, M., Sánchez Goñi, M.F., Litt, t. (eds.), The Climate of Past Interglacials, Developments in Quaternary Sciences, Elsevier, 7, 375–386.

Desprat, S., Sánchez Goñi, M.F., Duprat, J., Cortijo, E., and McManus, J.F. 2008. Millennial-scale climatic variability between 340 000 and 270 000 years ago in SW Europe: evidence from a NW Iberian margin pollen sequence, Cli-mate of the Past Discussions, 4 (2), 375-414.

Dima, M., and Lohmann, G. 2004. Fundamental and derived modes of climate variability: concept and application to interannual timescales. Tellus A, 56 (3), 229–249.

Dima, M., and Lohmann, G. 2007. A Hemispheric Mecha-nism for the Atlantic Multidecadal Oscillation. Journal of Climate, 20, 2706-2719.

Dong b.W., and Sutton R.t. 2002. Adjustment of the coupled ocean–atmosphere system to a sudden change in the thermohaline Circulation. Geophysical Research Letters, 29 (15), 1728.

Elkibbi M., and Rial, J.A. 2001. An outsider’s review of the astronomical theory of the climate: is the eccentricity-driven insolation the main driver of the ice ages? earth-science Reviews, 56, 161–177.

Elliot, M., Labeyrie, L., and Duplessy, J.C. 2002. Changes in North Atlantic deep-water formation associated with the Dansgaard–Oeschger temperature oscillations (60–10ka), Quaternary science Reviews, 21, 1153–1165.

Enfield, D.b., Mestas-Nuñez, A.M., and trimble, P.J. 2001. the Atlantic multidecadal oscillation and its relation to rain-fall and river flows in the continental U.S. Geophysical Research Letters, 28, 2077–2080.

EPICA project members 2004. Eight glacial cycles from an Antarctic ice core. nature, 429, 623-628.

EPICA project members 2006. One-to-one coupling of gla-cial climate variability in Greenland and Antarctica. na-ture, 444, 195-198.

Fanning, A.F., and Weaver, A.J. 1997. temporal geographical meltwater influences on the North Atlantic Conveyor: im-plications for the Younger Dryas. Paleoceanography, 12, 307–20.

Feng, S., Hu, Q., and Oglesby, R.J. 2009. AMO-like variations of Holocene sea surface temperature in the North Atlantic Ocean. Climate of the Past Discussion, 5, 2465–2496.

Ganopolski, A., and Rahmstorf, S. 2001. Rapid changes of glacial climate simulated in a coupled climate model. na-ture, 409, 153– 158.

Ganopolski, A,. and Rahmstorf, S. 2002. Abrupt glacial cli-mate change due to stochastic resonance. Physical Re-view Letters, 88 (3), 0385011– 0385014.

Gershunov, A., and barnett, t.P. 1998. ENSO influence on intraseasonal extreme rainfall and temperature frequen-cies in the contiguous United States: Observations and model results. Journal of Climate, 11, 1575–1586.

Giraudeau, J., Cremer, M., Manthé, S., Labeyrie, L., and bond, G. 2000. Coccolith evidence for instabilities in sur-face circulation south of Iceland during Holocene times. earth and Planetary science Letters, 179, 257-268.

Goodwin, P., Williams, R.G., Ridgwell, G., and Follows A.M.J. 2009. Climate sensitivity to the carbon cycle modulated by past and future changes in ocean chemistry. nature Geoscience, 2, 145 – 150.

Goosse, H., Arzel, O., Luterbacher, J.E., Renssen, H., Ried-wyl, N., timmermann, A., Xoplaki, E., and Wanner, H. 2006. the origin of the European “Medieval Warm Peri-od”, Climate of the Past Discussions, 2, 99–113.

Gray, S.t., Graumlich, L., betancourt, J., and Pederson, G.t. 2004. A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D. Geophysical Re-search Letters, 31, L12205, doi:10.1029/2004GL019932.

Grootes, P.M., and Stuiver M. 1997. Oxygen 18/16 variabil-ity in Greenland snow and ice with 10(-3)- to 10(5)-year time resolution. Journal of Geophysical Research, 102C, 26455–70.

Grousset, F.E., Labeyrie, L., Sinko, J.A., Cremer, M., bond, G., Duprat, J., Cortijo, E., and Huon, S. 1993. Patterns of ice rafted detritus in the Glacial North Atlantic (40-55ºN). Paleoceanography, 8 (2), 175-192.

Grousset, F.E., Cortijo, E., Huon, S., Hervé, L., Richter, t., burdloff, D., Duprat, J., and Weber, O. 2001. Zooming in on Heinrich layers. Paleoceanography, 16 (3), 240-259.

Harris, S.E., and Mix, A.C. 1999. Pleistocene precipitation balance in the Amazon basin recorded in Deep Sea Sedi-ments, Quaternary Research, 51, 14–26.

301


Hays, J.D., Imbrie, J., and Shackleton, N.J. 1976. Variations in the Earth’s orbit: pacemaker of the ice ages. science, New Series, 194 (4270), 1121-1132.

Heinrich, H. 1988. Origin and consequences of cyclic ice rafting in the northeast Atlantic Ocean during the past 130,000 years. Quaternary Research, 29 (2), 142–152.

Hendy, I.L., and Kennett, J.P. 2003. tropical forcing of North Pacific intermediate water distribution during Late Qua-ternary rapid climate change?. Quaternary science Re-views, 22, 673–689.

Hernández-Almeida, I., Sierro, F.J., Cacho, I., and Flores, J.A. 2012. Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene transition. Paleoceanography, 27 (3), DOI: 10.1029/2011PA002209.

Hinnov, L.A., Schulz, M., and Yiou, P. 2002. Interhemispheric space-time attributes of the Dansgaard-Oeschger oscilla-tions between 100 and 0 ka. Quaternary science Reviews, 21,1213– 28.

Hurrell, J.W. 1995. Decadal trends in the North Atlantic Oscil-lation regional temperatures and precipitation. science-AAAS-Weekly Paper Edition, 269, 676-679.

Hurrell, J.W., Kushnir, Y., and Visbeck, M. 2001. the North At-lantic Oscillation. science, 291 (5504), 603-605.

Hurrell, J.W., Kushnir, Y., Ottersen, G., and Visbeck, M. 2003. The north Atlantic Oscillation: climatic significance and environmental impact. Geophysical Monograph Series, 134, 279 pp.

Huybers, P.J. 2004. Comments on ‘Coupling of the hemi-spheres in observations and simulations of glacial cli-mate change’ by Schmittner, A., Saenko, O.A., and Weav-er, A.J. (Correspondence), Quaternary science Reviews, 23, 207–212.

Huybers, P.J. 2007. Glacial variability over the last two mil-lion years: an extended depth-derived age model, contin-uous obliquity pacing, and the Pleistocene progression. Quaternary science Reviews, 26 (1-2), 37-55.

Huybers, P.J. 2009. Pleistocene glacial variability as a cha-otic response to obliquity forcing. Climate of the Past Dis-cussions, 5 (3), 481-488.

Imbrie, J., and Imbrie, J.Z. 1980. Modeling the climatic re-sponse to orbital variations. science, New Series, 207 (4434), 943-953.

Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., and Shackle-ton, N.J. 1984. the orbital theory of Pleistocene climate: Support from a revised chronology of the marine delta 18O record. In: berger, A., Imbrie, J., Hays, H., Kukla, G., and Saltzman, b. (eds.), Milankovitch and Climate: under-standing the response to astronomical forcing, Proceed-ings of the NAtO Advanced Research Workshop held 30 November - 4 December, 1982 in Palisades, NY., D. Reidel Publishing, Dordrecht, 269.

Johnsen, S.J., Clausen, H.b., Dansgaard, W., Gundestrup, K.F.N., Hammer, C.U., Iversen, P., Jouzel, J., Stauffer, b., and Steffensen, J.P. 1992. Irregular glacial interstadials recorded in a new Greenland ice core, nature, 359, 311–313.

Jouzel, J., Petit, J.R., Souchez, R., barkov, N.I., Lipenkov, V. Ya., Raynaud, D., Stievenard, M., Vassiliev, N.I., Verbeke,

V., Vimeux, F. 1999. More than 200 meters of lake ice above subglacial Lake Vostok, Antarctica. science, 286 (5447), 2138-2141.

Jullien, E., Grousset, F., Malaizé, b., Duprat, J., Sanchez-Goñi, M.F., Eynaud, F., Charlier, K., Schneider, R., bory, A., bout, V., and Flores, J.A. 2007. Low-latitude “dusty events” vs. high-latitude “icy Heinrich events”. Quaternary Research, 68, 379–386.

Jungclaus, J.H., Haak, H., Latif, M., and Mikolajewicz, U. 2005. Arctic-North Atlantic interactions and multidecadal variability of the meridional overturning circulation. Jour-nal of Climate,18, 4013-4031.

Kanfoush, S.L., Hodell, D.A., Charles, C.D., Guilderson, t.P., Mortyn, G., and Ninnemann, U.S. 2000. Millennial-scale instability of the Antarctic Ice Sheet during the Last Gla-ciation. science, 288, 1815-1818.

Kennett, J.P., Cannariato, K.G., Hendy, I.L., and behl, R.J. 2000. Carbon isotopic evidence for methane hydrate in-stability during Quaternary interstadials. science, 288, 128-133.

Kerr, R.A. 2000. A North Atlantic pacemaker for the centu-ries. science, 288, 1984–1986.

Khider, D., Stott, L.D., Emile-Geay J., thunell, R, and Ham-mond, D.E. 2011. Assessing El Niño Southern Oscillation variability during the past millennium. Paleoceanogra-phy, 26, 3222-42.

Kidson, J.W. 1988. Interannual variations in the Southern Hemisphere Circulation. Journal of Climate, 1, 1177-1198.

Knight, J.R., Allan, R.J., Folland, C.K., Vellinga, M., and Mann, M.E. 2005. A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Re-search Letters, 32, L20708, doi:10.1029/2005GL024233.

Knorr, G., and Lohmann, G. 2003. Southern Ocean origin for the resumption of Atlantic thermohaline circulation dur-ing deglaciation. nature, 424, 532-536.

Knutti, R., Flückiger, J., Stocker, t. F., and timmermann, A. 2004. Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation. na-ture, 430, 851–856.

Knutti, R, and Hegerl, G.C. 2008. the equilibrium sensitivity of the Earth’s temperature to radiation changes. nature Geoscience, 1, 735–743.

Koutavas, A., deMenocal, P.b., Olive, G.C., and Lynch-Stieg-litz, J. 2006. Mid-Holocene El Niño–Southern Oscillation (ENSO) attenuation revealed by individual foraminifera in eastern tropical Pacific sediments. Geology, 34 (12), 993-996.

Kumar, K.K., Rajagopalan, b., and Cane, M.A. 1999. On the weakening relationship between the Indian monsoon and ENSO. science, 284 (5423), 2156-2159.

Lenton, t.M., Held, H., Kriegler, E., Hall, J.W., Lucht, W., Rahm-storf, S., and Schellnhuber, H.J. 2008. tipping elements in the Earth’s climate system. Proceedings of the national Academy of sciences of usA, 105 (6), 1786–1793.

Larrasoaña, J.C., Roberts A.P., Rohling, E.J., Winklhofer, M., Wehausen, R. 2003. three million years of monsoon vari-ability over the northern Sahara. Climate Dynamics, 21, 689–698.

Latif, M., Roeckner, E., botzet, M., Esch, M., Haak, H., Hage-mann, S., Jungclaus, J., Legutke, S., Marsland, S., and

302


Mikolajewicz, U. 2004. Reconstructing, monitoring, and predicting multidecadal-scale changes in the North At-lantic thermohaline circulation with sea surface tempera-ture. Journal of Climate, 17, 1605–1614.

Latif, M., boning, C.W., and Willebrand, J. 2007. Decadal to multidecadal variability of the Atlantic MOC: Mechanisms and predictability. In: Schmittner, A., Chiang, J.C.H., Hem-ming, S.R. (eds.), Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Over-turning, AGU Monograph, Vol. 173, American Geophysi-cal Union, Washington DC, 149-166.

Lebreiro, S.M., Francés, G., Abrantes, F., Diz, P., bartels-Jons-dottir, H., Stroynowski, S., Gil, I., Pena, L., Rodrigues, t., Nombela, M.A., Alejo, I., briffa, K., Jones, P., and Har-ris, I. 2006. Last two millennia coastal hydrographic and climate changes in the Atlantic Iberian margin (tagus Prodelta and Muros Ría). The Holocene, 16 (7), 999-1011.

Lebreiro, S.M., Moreno, J.C., McCave, I.N., and Weaver, P.P.E. 1996. Evidence for Heinrich layers off Portugal (tore Seamount: 39ºN, 12ºW). Marine Geology, 131, 47-56.

Lebreiro, S.M., Voelker, A.H.L., Vizcaino, A., Abrantes, F.G., Alt-Epping, U., Jung, S., thouveny, N., Gràcia, E. 2009. Sediment instability on the Portuguese continental mar-gin under abrupt glacial climate changes (last 60 kyr). Quaternary science Reviews, 28, 3211–3223.

Leduc, G., Vidal, L., tachikawa, K., bard, E. 2009. ItCZ rather than ENSO signature for abrupt climate changes across the tropical Pacific? Quaternary Research, 72 (1), 123–131.

Lenton, t.M., Held, H., Kriegler, E., Hall, J.W., Lucht, W., Rahms-torf, S., and Schellnhuber, H.J. 2008. tipping elements in the Earth’s climate system. Proceedings of the national Academy of sciences of the usA, 105 (6), 1786-1793.

Leuschner, D.C., and Sirocko, F. 2003. Orbital insolation forc-ing of the Indian Monsoon – a motor for global climate changes?. Palaeogeography, Palaeoclimatology, Palaeoe-cology, 197 (1–2), 83–95.

Lisiecki, L.E, and Raymo, M.E. 2005. A Pliocene-Pleis-tocene stack of 57 globally distributed benthic d18O records. Paleoceanography, 20, PA1003, 17 pp, doi:10.1029/2004PA001071.

Lisiecki, L.E., and Raymo, M.E. 2007. Plio–Pleistocene climate evolution: trends and transitions in glacial cycle dynam-ics. Quaternary science Reviews, 26 (1–2), 56–69.

Little, M.G., Schneider, R.R., Kroon, D., Price, b., Summer-hayes, C.P., and Segl, M. 1997. trade wind forcing of up-welling, seasonality, and Heinrich events as a response to sub-Milankovitch climate variability. Paleoceanography, 12 (4), 568-76.

Lohmann, G., Rimbu, N., and Dima, M. 2004. Climate signa-ture of solar irradiance variations: analysis of long-term instrumental, historical, and proxy data. International Journal of Climatology, 24, 1045–1056.

Lorenz, S.J., Kim, J.H., Rimbu, N., and Schneider, R.R. 2006. Orbitally driven insolation forcing on Holocene climate trends: Evidence from alkenone data and climate modeling. Paleoceanography, 21, PA1002, doi:10.1029/2005PA001152.

Loutre, M.F., and berger, A. 2003. Marine Isotope Stage 11 as an analogue for the present interglacial. Global and Planetary Change, 36 (3), 209–217.

Loulergue, L., Schilt, A., Spahni, R., Masson-Delmotte, V., blunier, t., Lemieux, b., barnola, J.-M., Raynaud, D., Stoc-ker, t.F., and Chappellaz, J. 2008. Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years. Nature, 453, 383-386.

Lozier, M.S. 2010. Deconstructing the Conveyor belt. scien-ce, 328, 1507-15.

Lüthi, D., Le Floch, M., bereiter, b., blunier, t., barnola, J.-M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K., and Stocker, t.F. 2008. High-resolution car-bon dioxide concentration record 650,000–800,000 years before present. nature, 453, 379-382.

Mann, M.E., Park, J., and bradley, R.S. 1995. Global inter-decadal and Century-scale climate oscillations during the past five centuries. nature, 378, 266-270.

Manabe, S., and Stouffer, R.J. 1997. Coupled ocean-atmo-sphere model response to freshwater input: comparison to Younger Dryas event. Paleoceanography, 12, 321–36.

Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M., and Fran-cis, R.C. 1997. A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin American Meteorological society, 78, 1069–1079.

Margari, V., Skinner, L.C., tzedakis, P.C., Ganopolski, A., Vautravers, M., and Shackleton, N.J. 2010. the nature of millennial-scale climate variability during the past two glacial periods. nature Geoscience, 3, 127 – 131.

Marshall, J., Kushnir, Y., battisti, D., Chang, P., Czaja, A., Dickson, R., Hurrell, J., McCartneyg, M., Saravan, R., and Visbeck, M. 2001. Review: North Atlantic climate variabil-ity: phenomena, impacts and mechanisms. International Journal of Climatology, 21, 1863-1898.

Martrat, b., Grimalt, J.O., Lopez-Martinez, C., Cacho, I. , Sie-rro, F.J., Flores, J.A., Zahn, R., Canals, M., Curtis, J.H., and Hodell, D.A. 2004. Abrupt temperature changes in the Western Mediterranean over the Past 250,000 Years. sci-ence, 306, 1762-1765.

Mayewski, P.A., Meeker, L.D., twickler, M.S., Whitlow, S., and Yang, Q.Z. 1997. Major features and forcing of high-latitude northern hemisphere atmospheric circulation us-ing a 110,000-year-long glaciochemical series. Journal of Geophysical Research, 102C, 26345–66.

Mayewski, P.A., Rohling, E.E., Stager, J.C., Karlén, W., Ma-ascha, K.A., Meeker, L.D., Meyerson, E.A., Gasse, F., van Kreveld, S., Holmgren, K., Lee-thorp, J., Rosqvist, G., Rack, F., Staubwasser, M., Schneider, R.R., and Steig, E.J. 2004. Holocene climate variability. Quaternary Research, 62 (3), 243-255.

McManus, J.F., bond G.C., broecker, W.S., and Johnsen, S. 1994. High-resolution climate records from the North At-lantic during the last interglacial. nature, 371, 326-329.

McManus, J.F., Oppo, D.W., and Cullen, J.L. 1999. A 0.5-mil-lion-year record of millennial-scale climate variability in the North Atlantic. science, 283, 971-975.

Mestas-Nuñez, A. and, Enfield, D.b. 2001. Eastern Equato-rial Pacific SSt variability: ENSO and non-ENSO compo-nents and their climatic associations. Journal of Climate, 14, 391-402.

Milankovitch, M. 1941. Canon of Insolation and the Ice Age Problem (in German), Math. natural science, 33, Spec. Publ. 132, R. Serbian Science, belgrade. (English transla-

303


tion by Israel Program for Science translation, Jerusalem, 1969), 633 pp.

Minobe, S. 1997. A 50–70 year climatic oscillation over the North Pacific and North America. Geophysical Research Letters, 24, 683– 686.

Mitchell, J.F.b, Lowe, J., Wood, R.A., and Vellinga, M. 2006. Extreme events due to human-induced climate change. Philosophical Transactions of the Royal society of Lon-don A, 364, 2117-2133.

Moreno, A., Cacho, I., Canals, M., and Sanchez-Vidal, A. 2004. Millennial-scale variability in the productivity sig-nal from the Alboran Sea record, Western Mediterranean Sea. Palaeogeography, Palaeoclimatology, Palaeoecol-ogy, 211, 205– 219.

Muller, R.A., and MacDonald, G.J. 1997. Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity. Pro-ceedings of the national Academy of sciences of usA, 94, 8329–8334.

Naughton, F., Sánchez Goñi, M.F., Kageyama, M., bard, E., Duprat, J., Cortijo, E., Desprat, S., Malaizé, b., Joly, C., Rostek, F., turon, J.-L. 2009. Wet to dry climatic trend in north-western Iberia within Heinrich events. earth and Planetary science Letters, 284 (3–4), 329–342.

Ogi, M., Yamazaki, K., and tachibana, Y. 2003. Solar cycle modulation of the seasonal linkage of the North Atlantic Oscillation (NAO). Geophysical Research Letters, 30 (22), 2170-74.

Ogurtsov, M.G., Nagovitsyn, Y.A., Kocharov, G.E., and Jung-ner, H. 2002. Long-period cycles of the Sun’s activity re-corded in direct solar data and proxies. solar Physics, 211, 371–394.

Oppo, D.W., Keigwin, L.D., and McManus, J.F. 2001. Persist-ent suborbital climate variability in marine isotopes. Pale-oceanography, 16 (3), 280-292.

Oppo, D.W., Linsley, b.K., Rosenthal, Y., Dannenmann, S., and beaufort, L. 2003, Orbital and suborbital cli-mate variability in the Sulu Sea, western tropical Paci-fic. Geochemistry, Geophysics, Geosystems, 4 (1), 1003, doi:10.1029/2001GC000260.

Paillard, D. 2001. Glacial cycles: toward a new paradigma. Reviews of Geophysics, 39 (3), 325–346.

Paillard, D., and Parreni, F. 2004. the Antarctic ice sheet and the triggering of deglaciations. earth and Planetary sci-ence Letters, 227, 263– 271.

Pailler, D., and bard, E. 2002. High frequency palaeoceano-graphic changes during the past 140 000 yr recorded by the organic matter in sediments of the Iberian Margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 181, 431-452.

Pelejero, C., Calvo, E., Logan, G.A, and De Deckker, P. 2003. Marine Isotopic Stage 5e in the Southwest Pacific: Simi-larities with Antarctica and ENSO inferences. Geophysi-cal Research Letters, 30, 2185-90.

Pena, L.D., Cacho, I., Ferretti, P., and Hall, M.A. 2008. El Niño–Southern Oscillation–like variability during glacial termi-nations and interlatitudinal teleconnections. Paleocea-nography, 23, PA3101-9, doi:10.1029/2008PA001620.

Peng, S., and Robinson, W.A. 2001. Relationships between atmospheric internal variability and the responses to an

extratropical SSt anomaly. Journal of climate, 14, 2943-2959.

Peterson, L.C., Haug, G.H., Hughen, K.A., and Röhl, U. 2000. Rapid changes in the hydrologic cycle of the tropical At-lantic during the last glacial. science, 290, 1947-51.

Rahmstorf, S. 2002. Ocean circulation and climate during the past 120,000 years. nature, 419, 207-214.

Rahmstorf, S. 2003. timing of abrupt climate change: A pre-cise clock, Geophysical Research Letters, 30 (10), 1510, doi:10.1029/2003GL017115.

Rahmstorf, S., Crucifix, M., Ganopolski, A., Goosse, H., Ka-menkovich, I., Knutti, R., Lohmann, G., Marsh, R., Mysak, L.A., Wang, Z., and Weaver, A.J. 2005. thermohaline circu-lation hysteresis: a model intercomparison. Geophysical Research Letters, 32:L23605, doi:10.1029/2005GL023655.

Raymo, M.E. 1997. the timing of major climate terminations. Paleoceanography, 12 (4), 577-585.

Rayner, N.A., Parker, D.E., Horton, E.b., Folland, C.K., Alexander, L.V., Rowell, D.P., Kent, E.C., Kaplan, A. 2003. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. Journal of Geophysical Research, 108, 4407, 29, doi:10.1029/2002JD002670.

Rial, J.A., and Anaclerio, C.A. 2000. Understanding nonlin-ear responses of the climate system to orbital forcing. Quaternary science Reviews, 19, 1709–1722.

Rial, J.A., and Yang, M. 2007. Is the frequency of abrupt cli-mate change modulated by the orbital Insolation?. In: Schmittner, A., Chiang, J.C.H., Hemming, S.R. (eds.), Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Overturning, AGU Mono-graph, Vol. 173, American Geophysical Union, Washing-ton DC, 167–174.

Rodwell, M.J., Rowell, D.P., and Folland, C.K. 1999. Oceanic forcing of the wintertime North Atlantic Oscillation and European climate. nature, 398, 320-323.

Romero, O.E., Leduc, G., Vidal, L., Fisher, G. 2011, Millen-nial variability and long-term changes of the diatom production in the eastern equatorial Pacific during the last glacial cycle, Paleoceanography, 26, PA2212, doi:10.1029/2010PA002099.

Rousseau, D.D., Kukla, G., and McManus, J. 2006. What is what in the ice and the ocean? Quaternary science Re-views, 25 (17–18), 2025–2030.

Rosenthal, Y., Oppo, D.W., and Linsley, b.K. 2003. the am-plitude and phasing of climate change during the last deglaciation in the Sulu Sea, western tropical Pacific. Geochemistry, Geophysics, Geosystems, 30 (8), 1428, doi:10.1029/2002GL016612.

Ruddiman, W.F., and McIntyre, A. 1981. Oceanic mechanisms for amplification of the 23,000 year ice-volume cycle. science, 212 (4495), 617–627.

Ruddiman, W.F., and Raymo, M.E. 2003. A methane-based time scale for Vostok ice. Quaternary science Reviews, 22 (2–4), 141–155.

Sakai, K., and Peltier, W.R. 1999. A dynamical system model of the Dansgaard-Oeschger oscillation and the origin of the bond Cycle. Journal of Climate, 12, 2238-2255.

Saikku, R., Stott, L., and thunell, R. 2009. A bi-polar signal recorded in the western tropical Pacific: Northern and

304


Southern Hemisphere climate records from the Pacific warm pool during the last Ice Age. Quaternary science Reviews, 28 (23-24), 2374-2385.

Sánchez Goñi, M.F., Cacho, I., turon, J.-L, Guiot, J., Sierro, F.J., Peypouquet, J.-P., Grimalt, J.O., Shackleton, N.J. 2002. Synchroneity between marine and terrestrial re-sponses to millennial scale climatic variability during the last glacial period in the Mediterranean region, Climate Dynamics,19, 95–105.

Santer, b.D., Mears, C., Doutriaux, C., Caldwell, P., Gleckler, P.J., Wigley, t.M.L., Solomon, S., Gillett, N.P., Ivanova, D., Karl, t.R., Lanzante, J.R., Meehl, G.A., Stott, P.A., taylor, K.E., thorne, P.W., Wehner, M.F., and Wentz, F.J. 2011. Sepa-rating signal and noise in atmospheric temperature chang-es: the importance of timescale. Journal of Geophysical Research, 116, D22105, 19 doi:10.1029/2011JD016263.

Sarnthein, M., Jansen, E., Weinelt, M., Arnold, M., D uplessy, J.-C., Erlenkeuser, H., Flatøy, A., Johannessen, G., Johan-nessen, t., Jung, S., Koc, N., Labeyrie, L., Maslin, M., Pflaumann, U., and Schulz, H. 1995. Variations in Atlantic surface ocean paleoceanography, 50º–80ºN—A time-slice record of the last 30,000 years. Paleoceanography, 10, 1063–94.

Sarnthein, M., Van Kreveld, S., Erlenkeuser, H., Grootes, P., Kucera, M., Pflaumann, U., and Schulz, M. 2003. Centen-nial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western barents shelf, 75ºN. Boreas, 32 (3), 447–461.

Schaefer, G., Rodger, J.S., Hayward, b.W., Kennett, J.P., Sabaa, A.t., and Scott, G.H. 2005. Planktic foraminiferal and sea surface temperature record during the last 1 Myr across the Subtropical Front, Southwest Pacific. Marine Micropaleontology, 54, 191– 212.

Schlesinger, M.E., and Ramankutty, N. 1994. An oscillation in the global climate system of period 65–70 years. nature, 367, 723-726.

Schmittner, A., Chiang, J.C.H., and Hemming, S.R. 2007. Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Overturning, AGU Mono-graph, Vol. 173, American Geophysical Union, Washing-ton DC, 392 pp.

Schmittner, A., Saenko, O.A., and Weaver, A.J. 2003. Cou-pling of the hemispheres in observations and simulations of glacial climate change. Quaternary science Reviews, 22 (5–7), 659–671.

Schulz, M. 2002a. the tempo of climate change during Dans-gaard-Oeschger interstadial and its potential to affect the manifestation of the 1470-year climate cycle. Geophysi-cal Research Letters, 29, doi:10.1029/2001GL013277.

Schulz, M., and Paul, A. 2002. Holocene climate variability on centennial-to-millennial time scales: 1. Climate records from the North-Atlantic realm, In: Wefer, G., berger, W., behre, K.-E., and Jansen, E. (eds.). Climate Development and History of the north Atlantic Realm. Springer-Verlag, berlin, Heidelberg, 41-54.

Seager, R., Kushnir, Y., Naik, N.H., Cane, M.A., Muller, J. 2001. Wind-Driven shifts in the latitude of the Kuroshio-Oyashio extension and generation of SSt anomalies on decadal timescales. Journal of Climate, 14, 4249-4265.

Severinghaus, J.P. 2009. Southern see-saw seen. nature, 457, 1093-1094.

Shabalova, M.V., and Weber, S.L. 1999. Patterns of tempera-ture variability on multidecadal to centennial timescales. Journal of Geophysical Research, 104, D24, 31023-31041.

Shackleton, N., Hall, M.A., and Vincent, E. 2000. Phase rela-tionships between millennial-scale events 64,000 –24,000 years ago. Paleoceanography, 15 (6), 565–569.

Siddall, M., Stocker, t.F., blunier, t., Spahni, R., Schwander, J., barnola, J.-M., and Chappellaz, J. 2007. Marine Isotope Stage (MIS) 8 millennial variability stratigraphically iden-tical to MIS 3. Paleoceanography, 22, PA1208, 4 PP.

Sierro, F.J., Hodell, D.A., Curtis, J.H., Flores, J.A., Reguera, I., Colmenero-Hidalgo, E., bárcena, M. A., Grimalt, J.O., Cacho, I., Frigola, J,. and Canals, M. 2005. Impact of ice-berg melting on Mediterranean thermohaline circulation during Heinrich events. Paleoceanography, 20, PA2019, doi:10.1029/2004PA001051.

Skinner, L.C., and Elderfield, H. 2007. Rapid fluctua-tions in the deep North Atlantic heat budget during the last glacial period. Paleoceanography, 22, PA1205, doi:10.1029/2006PA001338.

Skinner, L.C., Elderfield, H., and Hall, M. 2007. Phasing of millennial climate events and Northeast Atlantic deep-water temperature change since 50 ka bP. In: Schmittner, A., Chiang, J.C.H., Hemming, S.R. (eds.), Ocean Circula-tion: Mechanisms and Impacts—Past and Future Chang-es of Meridional Overturning, AGU Monograph, Vol. 173, American Geophysical Union, Washington DC, 197-208.

Steig, E.J., and Alley, R.b. 2002. Phase relationships be-tween Antarctic and Greenland climate records. Annals of Glaciology, 35, 451–56.

Stenni, b., Masson-Delmotte, V., Johnsenet, S., and Jouzel, J. 2001. An oceanic cold reversal during the last deglacia-tion, science, 293, 2074-2077.

Stenni, b., buiron, D., Frezzotti, M., Albani, S., barbante, C., bard, E., barnola, J.M., baroni, M., baumgartner, M., bonazza, M., Capron, E., Castellano, E., Chappellaz, J., Delmonte, b., Falourd, S., Genoni, L., Iacumin, P., Jouzel, J., Kipfstuhl, S., Landais, A., Lemieux-Dudon, b., Maggi, V., Masson-Delmotte, V., Mazzola, C., Minster, b., Monta-gnat, M., Mulvaney, R., Narcisi, b., Oerter, H., Parrenin, F., Petit, J.R., Ritz, C., Scarchilli, C., Schilt, A., Schüpbach, S., Schwander, J., Selmo, E., Severi, M., Stocker t.F., and Udisti, R. 2010. Expression of the bipolar see-saw in An-tarctic climate records during the last deglaciation: na-ture Geoscience, 4 (1), 46–49.

St-Onge, G., Stoner, J.S., and Hillaire-Marcel, C. 2003. Holocene paleomagnetic records from the St. Lawrence Estuary, eastern Canada: centennial-to millennial-scale geomagnetic modulation of cosmogenic isotopes. earth and Planetary science Letters, 209 (1–2), 113–130.

Stocker, t. 1998. the seesaw effect. science, 282, 61–62.Stocker, t.F. 2000. Past and future reorganizations in the cli-

mate system. Quaternary science Reviews, 19, 301-319.Stocker, t.F. 2002. North South connections. science, 297,

1814-1815.Stocker, t.F., and Johnsen, S.J. 2003. A minimum thermo-

dynamical model for the bipolar seesaw. Paleoceanogra-phy, 18 (4), 1087, doi: 10.1029/2003PA000920.

305


Stocker, t.F., and Mysak, L.A. 1992. Climatic fluctuations on the century time scale: A review of high-resolution proxy data and possible mechanisms. Climatic Change, 20 (3), 227-250.

Stocker, t.F., and Wright, D.G. 1991. Rapid transitions of the ocean’s deep circulation induced by changes in surface water fluxes. nature, 351, 729-31.

Stott, L., Poulsen, C., Lund, S., and thunell, R. 2002. Super ENSO and global climate oscillations at millennial time scales. science, 297 (5579), 222-226.

tiedemann, R., and Mix, A. 2007. Leg 202 synthesis: Southeast Pacific paleoceanography. In: tiedemann, R., Mix, A.C., Richter, C., and Ruddiman, W.F. (eds.), Proc. ODP, sci. Results, 202: College Station, tX (Ocean Drilling Program), 1–56. doi:10.2973/ odp.proc.sr.202.201.2007.

timmermann, A., Latif, M., Voss, R., and Grotzner, A. 1998. Northern hemispheric interdecadal variability: a coupled air-sea mode. Journal of Climate, 11, 1906-1931.

timmermann, A., and Goosse, H. 2004. Is the wind stress forcing essential for the meridional overturning circu-lation? Geophysical Research Letters, 31, L04303, 4 pp, doi:10.1029/2003GL018777.

timmermann, A., An, S.I., Krebs, U., and Goosse, H. 2005. ENSO Suppression due to Weakening of the North At-lantic thermohaline Circulation. Journal of Climate, 18, 3122-39.

tjallingii, R., Claussen, M., Stuut, J.-b., Fohlmeister, J., Jahn, A., bickert, t., Lamy, F., and Rohl, U. 2008. Coherent high- and low-latitude control of the northwest African hydro-logical balance. nature Geoscience, 1, 670-675.

trouet, V., Esper, J., Graham, N.E., baker, A., Scourse, J.D., and Frank, D.C. 2009. Persistent positive North Atlantic Oscillation mode dominated the Medieval Climate Anom-aly. science, 324, 78-80.

tudhope, S. , and Collins, M. 2003. the past and future of El Niño. nature, 424, 261-262.

tzedakis, P.C., Frogley, M.R., Lawson, I.t., Preece, R.C., Ca-cho, I., and de Abreu, L. 2004. Ecological thresholds and patterns of millennial-scale climate variability: the re-sponse of vegetation in Greece during the last glacial pe-riod. Geology, 32 (2), 109–112.

tziperman, E., and Gildor, H. 2003. On the mid-Pleistocene transition to 100-kyr glacial cycles and the asymmetry be-tween glaciation and deglaciation times, Paleoceanogra-phy, 18, 1001, 8 PP., doi:10.1029/2001PA000627.

van Kreveld, S.A., Knappertsbusch, M., Ottens, J., Ganssen, G.M.,and van Hinte, J.E. 1996. biogenic carbonate and ice-rafted debris (Heinrich layer) accumulation in deep-sea sediments from a Northeast Atlantic piston core. Ma-rine Geology, 131 (1–2), 21–46.

Vellinga, M., and Wu, P. 2004. Low latitude freshwater influ-ence on centennial variability of the Atlantic thermoha-line Circulation. Journal of Climate, 17 (23), 4498–4511.

Visser, K., thunell, R., and Stott, L. 2003. Magnitude and tim-ing of temperature change in the Indo-Pacific warm pool during deglaciation. nature, 421, 152-55.

Vidal, L., Labeyrie, L., Cortijo, E., Arnold, M., Duplessy, J.C., Michele, E., becqué, S., and van Weering, t.C.E. 1997. Evi-dence for changes in the North Atlantic Deep Water linked to meltwater surges during the Heinrich events. earth and Planetary science Letters, 146, 13-27.

Vidal, L., Labeyrie, L., and Van Weering, t.C.E. 1998. benthic d18O records in the North Atlantic over the last glacial pe-riod (60–10 kyr). Evidence for brine formation. Paleocean-ography, 13 (3), 245-251.

Visser, K., thunell, R., and Stott, L. 2003. Magnitude and tim-ing of temperature change in the Indo-Pacific warm pool during deglaciation, Nature, 421, 152-155.

Voelker, A.H.L. 2002. Global distribution of centennial-scale records for Marine Isotope Stage (MIS) 3: a database. Quaternary science Reviews, 21, 1185–212.

Voelker, A.H.L., Lebreiro, S.M., Schoenfeld, J., Cacho, I., Er-lenkeuser, H., Abrantes, F.F.G. 2006. Mediterranean out-flow strengthening during Northern Hemisphere Cool-ings: a salt source for the glacial Atlantic? earth Planetary science Letters, 245, 39–55.

Webster, P., and Yang, S. 1992. Monsoon and ENSO: selec-tively interactive systems, Q.J.R. Meteoroly society, 118, 877-926.

Wood, R.A., Vellinga, M., and thorpe, R. 2003. Global warm-ing and thermohaline circulation stability. Philosophical Transactions of the Royal society of London, 361 (1810), 1961-1975.

Wolter, K., and timlin, M.S. 1998. Measuring the strength of the ENSO events: How does 1997/98 rank?. Weather, 53 (9), 315-324.

Wu, L., Liu, Z. and Gallimore, R. 2003. Pacific decadal vari-ability: the tropical Pacific mode and the North Pacific mode. Journal of Climate, 16, 1101–1120.

Yu, J.Y., Mechoso, C.R., McWilliams, J.C., Arakawa, A. 2002. Impacts of the Indian Ocean on the ENSO cycle. Geophysi-cal Research Letters, 29 (8), 1204, 10.1029/2001GL014098.

Zachos, J., Pagani, M., Sloan, L., thomas, E., and billups, K. 2001. trends, rhythms, and aberrations in global climate 65 Ma to present. science, 292 (5517), 686-693.

Zhang, R., and Delworth, t.L. 2005. Simulated tropical re-sponse to a substantial weakening of the Atlantic ther-mohaline circulation. Journal of Climate, 18, 1853–60.

Zhang, R., and Delworth, t.L. 2007. Impact of the Atlan-tic Multidecadal Oscillation on North Pacific climate variability. Geophysical Research Letters, 34, L23708, doi:10.1029/2007GL031601.

Zhang, R., and Vallis, G.K. 2006. Impact of great salinity anomalies on the low-frequency variability of the North Atlantic climate. Journal of Climate, 19, 470-82.

Recibido: noviembre 2012Revisado: enero 2013Aceptado: febrero 2013Publicado: abril 2013

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